In my experience while alcohol can make you very uncoordinated and has the so-called 'liquid courage' effect, cannabis tends to only make the consumer enjoy what they already enjoyed more and differently, and rant about whatever ideas pop into their head. The first time I got really drunk, I had to be walked home and put in bed, then overslept and had a terrible hangover. The first time I got really high, I thought I was in a horror movie for half an hour, then played video games with my friends and had a religious experience listening to music and watching the iTunes visualizer. Cannabis in my opinion has less potential for both harm and abuse than alcohol.
There are many instances of people that are "mean drunks" yet, one never hears about somebody becoming violent while on marijuana.
Marijuana usually has a sedating effect on most users, however marijuana can cause fear, anxiety, panic or paranoia, which can result in an aggressive outburst.
Just like there are quiet drunks, there are people who are mean while on marijuana. But you can't forget the long term health effect of marijuana, cancer, respiratory problems, so it not fair to say it's a safe drug, but you can argue that it's a safer drug. Once we get some good long term data, I feel that it will be safer than alcohol.
Research that has come out so far seems to suggest that Marijuana does not cause cancer. In fact, so far it shows that it may even kill off cancer cells. I agree that more research is needed.
What you are probably seeing is the fact the most people who smoke marijuana don't smoke 20 joints a day (that a pack a cigarettes a day) The studies that have shown that marijuana might kill off cancer cell didn't show it was significant enough to say that, all they could say is maybe.
They may or may not smoke the marijuana to use it as a medicine or just for pleasure. A big problem with the sell of legal marijuana has been when it is in a bar or other food is the bar should only be eating one bite at a time. Some people are eating the whole bar like they would a candy bar and some have had to go to the hospital.
As others have commented the medical side effects may make marijuana a safer choice then the pills that have passed all the legal hurdles to be on the market. If the Feds would legalize or remove the class 1 it could be studied like any other drug for what is good and what is bad. On the recreation it can be good and bad just like alcohol. From what I have seen mean stoned users are rare.
For most, if not all of the medical effects cannabis has been found to have, it is my understanding of the situation that cannabis has fewer negative side effects than the alternatives. A good example for this is PTSD medication which causes liver problems. I agree that more research definitely needs to be done, but so far I am not aware of any data which suggests excessive caution is necessary around cannabis use in physically mature adults.