Not Military service, but civil service.
If you grow up for the vast majority of your life in a free democratic society you must realize that what made your country great is the people who live within it and worked to make it that way, in order for it to continue being great and grow and progress as a country those who took from it should give something back.
Civil service, which would include military training, would be a great way for citizens to give back to the countries that they call home and help improve the infrastructure and economy of their country.
No one should be forced to fight and possibly die for a cause they don't believe in, and is a great way to turn people against the government. Additionally I agree with u/Phoenix where (s)he stated under the no opinion, those forced to fight are not fit to fight, as most people forced to do something against their will (unless under extreme coersion) will not do a good job of it and may actually endanger other soldiers that are there for what they believe in.
Some military training should however be included in civil service as it would allow everyone to fight for their country if the need arose (ie an invasion) as well as provide excellent physical and mental training that is applicable to most situations. Additionally it would then allow those that felt like serving the country in war to do so, however I feel no one should be forced to kill or die simply because it's 'their patriotic duty'.