In terms of soldiers I believe there's three different types I've seen so far in my time:
First there's the sort that prove Mefustae's point, the ones that are too stupid to be scared. They're mostly the sort that join because every male in their family had been a soldier or had fought in every war before them. I've seen surprisingly few of these though, and they seem to be almost entirely Marines and Army.
Secondly, there's the type that join to get the benefits but are a little more iffy about combat/deployment than the first group. They join for the secure income after they drop out of college and can't find anything else to do. Fortunately most of these don't last long and a fair percentage wash out/are discharged during A School/Tech school.
Then there's the idealists. This is the group of people that joined out of patriotic/borderline nationalist fervor, are looking for a secure job that provides a good environment to raise a family and accept the fact that they will face deployment unlike the second group. Unlike thje first group that looks to deployment for glory, they tend to be the ones who see deployment as their chance to make a difference. They want to be the ones whose work saves lives and stops another terrorist attack.
Fortunately 75% of the folks that I have met during my time have been from the third set, from my Basic Training instructors to the officers out here in California, not to mention most of the new guys I've been with since Basic.
Lulz. Don't believe everything people say.
There is only one reason people join the army. It's always a combo of desperation and boredom (those two ARE one in this case, don't correct me). Desperation being not having any money and a ****ed up family (You don't see the rich kids with proper families volounteering much do ya? No, they have the family business to run, and infest the world with nepotism, or you know, masturbate in school until they're 30) and boredom is usually the part of not knowing what to do with your life and/or failing at most things you do, so you know, might as well join the army since bagging groceries is kind of shameful. Rather die from a bullet if you know what I mean.
Patriotism, benefits, stupidity, and all that are just words that are as worthless as they sound. Excuses to mask the above.
It's one of the reasons the USA pretty much lost every war since WW2. In WW2 everyone was taken to the battlefield, including the intelligent people, the people with rich parents (****, even the rich parents went), extensive educational backgrounds etc. were all in it to win it, and it worked so well because of the smart people. However later on the draft started excluding the college and graduate students, surely the rich as well (in wars that were really about something else completely than what was advertised) until the draft was revoked and only the poor indignant who didn't know any better were given the "choice" to go die in some desert or jungle for no real reason given whatsoever.
Nothing quite like desperation, hunger and lack of prospects to make one sign up. And it's not like this is only in the USA. It's like that over here too. Everywhere really.
It's why kids carry AK-47's in the third world. They start 'em early there, because prospects? Lulz. What prospects.