Unfortunately, the decision actually made the world less safe, and also consumed money that could have been used for education or healthcare. Not sure how complaining about teachers and doctors helps make society better, either.
Meanwhile, teaching and medicine still are making the world a better place.
So, if you just want to shoot guns, do it at home or a range or something. If you want to kill people, seek help. Neither make you a hero. But volunteering to teach the future or care for people? More likely does.
While a kid that goes and tries in the military is helping in one way or another. The military has better systems to extract value than the school districts.
So, let's get back on topic: some individuals glamorize going to iraq to shoot guns and kill random people so much, that they actually believe such killing urges are helpful. So I feel these individuals are doing a disservice because they aren't good at identifying what is helpful and what isn't.
Meanwhile, a kid that goes into teaching or medicine (you keep ignoring medicine. Curious.) is helping in one way or another. You're right that these iraq war volunteers extract value from society (and keep it for themselves). Teaching and medicine, on the other hand, have better systems to give that value back to society.