Don't equate veterans with assholes please? Yes there are asshole veterans.
However:
1) Forced conscription is a thing in many countries
2) Even in volunteer forces, there's lots of carrots on a stick they put out to get young people who don't know better to join.
3) People often force their children to enlist
4) Some people enlist because they have no other means to escape a horrible situation
5) Not every veteran flies the flag, is even patriotic, etc.