The evidence is to the contrary--middle class and above are over-represented in the US military.
"Their median family income is more than $73,000, compared with $66,000 for civilians, and recruits are most likely to come from families in the middle of the wealth distribution, with median wealth of $87,000, almost $10,000 more than civilians."
This is for enlisted members. It's probably safe to have some intuition that officers will skew wealthier.
Isn't "money for college and healthcare" kinda obvious about it? Like there's almost a wink and a nudge at the end of it.
It's super blatant that having very few economic options and no healthcare chooses fitness for service for you.