I can't answer for why Vagabond hates the military.
But, as a military person, I can state a reason or two why people have judged me/my job for that.
When some find out I'm in the military, it is often assumed that I'm a right-wing wing-nut head case who secretly wants American Imperialism to become reality, that we all want to go out and kill every Muslim or foreigner or take over every country that happens to be in a geopolitical area of interest.
Sometimes it's amusing because I'm a liberal who used to be married to a Muslim and who was against the Iraq War, but for Afghanistan.
Oh, and I've also heard "baby killer" which is an old holdover from the Vietnam era.