The term "politically correct" is a right-wing specter. I have never once in my life heard an informed activist for the LGBTQ movement, the civil rights and anti-racist movement, the feminist movement, etc. say to someone "We have to be politically correct". It doesn't work, it has a namby-pamby ring to it, it doesn't express the appropriate outrage, and it is frankly not appropriate for activism.
There are so many problems with the assertions against "PC" (I will now call them "basic courtesy and accuracy") arguments.
The most major one is that we are never discussing the mere use of a slur in isolation. Even when a comedian breaks decorum in some way that costs them popularity, like when Michael Richards (of Kramer fame) did it, no one was focusing just on the mere use of the n-word. It wasn't as if Richards said, "Man, isn't Al Sharpton cool? He's my ni**a". Rather, he said "Fifty years ago we'd have you upside-down with a f**king fork up your ass!" and "That's what happens when you interrupt the white man, don't you know?" In other words, Richards' rant was racial terrorism. He evoked some of the horrible atrocities that happened to people who were lynched, including being burnt with blowtorches and having pieces taken off, and he asserted his white supremacy and the degree to which he belonged. Yes, that was all still rhetoric, but it wasn't just the literal word: it was his aggressiveness against people of color.
Many defended Richards on this front. They defended him as if his opposition was just fetishizing a word, "ni**er", and giving it magical properties.
Of course, each time I write out that word, that word that has been used with hate, my stomach churns. See, whites have the privilege of viewing that word as just being a word. For blacks and even many other people of color (especially Native Americans, Arabs and Muslims, who have been roped into it by "prairie ni**er" and "sand ni**er"), it evokes five hundred years of history. It evokes hundreds of years where that word was bellowed in an effort to kill, enslave, bomb, hurt, lynch, burn, terrorize, and mangle people. It evokes hundreds of years of fear.
White folks routinely have the privilege of pretending history doesn't matter and doesn't echo. Even I, as the son of an immigrant, have to know better than that. I know supremacy has a life and a breath all of its own.
When people on the political left and center-left bring up that we should call people "transgender" and call them by the gender pronoun that matches their new gender identity, we aren't just saying that as an idle matter of decorum: we are saying it to people who want them to go into a bathroom that they will mentally and in many cases physically not belong, who want to cut their wages or kick them out of their community.
When people on the political left and center-left bring up that we should try to call "Mexicans" Chicana/os, Hispanics or Latina/os, we aren't just talking to people who insist on calling people from Mexico Mexicans: we are fighting against those who would call them rapists and drug dealers, as if the entire group was just one raping, drug dealing apparatus or entity, some tentacled monster.
When people on the political left and center-left insist that we should use gender-neutral language ("firefighters" rather than "firemen"), we aren't just fighting the rhetorical obliteration of females doing a job: we're also fighting those who think women can't be leaders because of their periods.
See, conservatives seem to think, "You've won everything! Can't you just leave the English language alone?"
Oh, no, brother (and it is so often a brother rather than a sister), you have it twisted.
In fact, we have so far to go, from anti-discrimination law to basic tolerance in public spaces to people actually being informed about atheists. We are fighting institutional discrimination, prejudice and bigotry stemming from institutional racism and white supremacy, homophobia and heteronormativity, sexism and male dominance, anti-atheist and agnostic bigotry and Christian hegemony, anti-immigrant and anti-global attitudes and American hegemony, and classism and the dominance of the rich. Notice how, in each case, I listed not just the group that was being targeted but the group that was being elevated. Every time someone says "This is a Christian nation", it is yet another rhetorical assertion of a dominance that they have come to expect and yet have no right to expect and have not earned because such an endeavor would be impossible. The sacrifices of Christians who came before gives no modern Christian a single claim to institutional supremacy. Their majority status does not either.
Even within the realm of language, we're not just making individual words taboo. When someone says "Blacks have lower IQ", they are repeating an essentialist, racist, bigoted, stereotypical notion of people of color as if they're in a spreadsheet. Even when there is some evidence supporting it, that evidence is never deployed honestly or consistently. And many times, such evidence is just outright false and dishonest. We are fighting people's racist, sexist, homophobic and xenophobic ideas of other human beings, arguing that other human beings are on average just as competent, decent, intelligent and kind as they are. And those biases are used to justify present inequities. The logic, even when it isn't stated out loud, goes, "Well, black people are criminals anyways, so why bother feeding their children?" or "Well, blacks are more likely to commit a homicide anyways, so why bother getting lead off the walls?" Once again, we can't separate language and cognition from political ideas. Martin Gilens, and researchers working in his vein, have repeatedly found that racist biases are massively deterministic of whether one is willing to support policies like welfare. Policy issues in America are racialized and sexualized. Masculine identity is part of militaristic policies, which in turn influences debates like gays and women in the military.
The second issue is that, even insofar as we're rectifying language, this is what societies do.
No society within the history of the planet has ever said that all language is equally appropriate in public parlance.
Most societies had very strong rules about what one could say in public. Honor codes, rules about courtesy that governed not just what hand one shook with (often as part of an effort to avoid contamination and the spread of germs even before people knew about the modern germ theory), kosher rules... the idea that there are certain things one does not say and do is common to history. Two of the Ten Commandments concern speech: Not taking the Lord's name in vein, and honoring one's mother and father.
One could argue that this was the case of feudal, monarchic and non-democratic societies. But that is emphatically false. Courtesy rules, manners books and so forth still exist. There are numerous 1950s shorts about the proper courtesy and rules for having a family dinner together. These emphatically include ways of talking and not talking: don't gossip, don't monopolize speech, don't put people off their lunch.
What astonishes me so much about this is the political cleavage. Naively, I would have thought that many conservatives, people who are concerned with courtesy and decorum, would naturally and easily come to accept that there are certain ways we should and should not speak as a normative fact. They would come to accept, "Ah, these human beings prefer to be addressed by the opposite gender. How boorish would it be not to accommodate it?" One would think it'd be punk leftists who would spit and say "They're a dude!"
But of course this is accepting conservative self-image and propaganda. In fact, the right-wing across history, the forces that preserve tradition, have always been perfectly able to be rude, cruel, and decidedly non-courteous. They just pretended otherwise as a thin veneer of civilization.
And challenging the entitlement (not the right but the sense that one should not face consequences) of those used to being afforded unlimited latitude challenges their supremacy. And when their supremacy is challenged, they are willing to get mighty rude.
Now, of course, is there a balance to be struck? Of course. Certain taboos should always be challenged. A transgressive attitude is always healthy at the right time and the right place. If friends are hanging out and talking, and there's a high degree of trust, then it can be reasonable to say some things one might not say in mixed company. And certainly artists, comedians, etc. need to be granted some leeway to break sacred cows without too much criticism in response.
But remember: So many of the same people who fight the "PC agenda" will loudly support Trump's support of seditious libel suits against journalists, loudly insist that one shouldn't use the Lord's name in vain, demand that the American flag never be burned or defaced, and insist that one should always "support the troops" no matter one's disagreements with American foreign policy.
And it is precisely that "high degree of trust" that is not to be taken for granted. When so many people are able to say "I'm not racist, I have a black friend", or otherwise signal that they're not "one of the bad ones" and should be given some latitude, they fundamentally misunderstand the trust people. People of color, women, LGBTQ individuals, atheists and agnostics... none of them can trust the rhetorical goodwill of someone they don't know.
The final point is precisely what the original questioner asked: "Others believe that being politically correct limits opinions, and will restrain them from conversing and interacting with others. Because of this, it will create a barrier between different groups, and do more harm then good".
In other words, for the need of social lubrication and discussion, once again people of color, women, LGBTQ folks, non-Americans, immigrants... they all must sacrifice their sense of humanity and how they wish people would speak to them for the good of society.
Never once must the dominant group sacrifice their own sense of comfort, even temporarily, in order to learn new language and to (much more importantly) unlearn their toxic, unfair biases.
Every human being has a right to say, "I demand to be treated with respect, and if you don't, I will not interact with you, I will not speak to you, and I will not do business with you". There is a bare minimum of treatment we can demand in order to interact with us in commerce and daily life.
Those who demand that people not correct other people's speech... are correcting other people's speech.
The anti-PC brigade have a fundamental hypocrisy: They say "I should be able to say anything I want, and you shouldn't be able to say anything you want".
To quote Jeremy Sherman's astute analysis: "By accusing people of being PC we try to persuade people to be less sensitive, less influenced by other people’s opinions, but in declaring PC a universal moral error, we pretend that we could live in a world where no one influences anyone. Usually we do it as a way of claiming our right to try to influence others without being influenced. It’s like the current libertarian craze, motivated by 'my freedom to say and do what I want, without getting hassled' If you want your freedom to say and do what you want, expect the same from everyone else. The person who accuses others of being PC has his own PC sensitivities. He’s saying it’s politically incorrect for you to be politically correct. Anti-PC and libertarianism are often rationalizations for dishing it out without having to take it in".
Either we accept that anything is okay to say or we accept that there should be voluntary rules that we choose, as civilized human beings, as to what we say or do not say. And if anything is okay to say, I get to tell someone else to shut up. If someone else gets to call a friend of mine the "n-word", I get to call them a monster who shouldn't show their face in public. If we're going to make society an endless war of words, then we get every weapon just like you do. Either way, the anti-PC crowd is wrong. Either way, they are demanding "My rules for thee but not for me".
See, what conservatives want is consequence-free speech, not free speech.
Not only is that not a right, not only is it a logical contradiction, but it is a moral absurdity.
You see, this entire battle is really a battle of entitlement against responsibility.
When we have rights as human beings, that gives us power. And with great power comes great responsibility.
If we have the right to choose how we speak, we have the duty to choose that speech carefully.
Those who argue against those calling on them to have respect and kindness for others are arguing to be moral children. They want the rights without the attendant responsibilities.
That is not good for them. And it must be obliterated as an idea.