While I agree with you on who joins up, I think they are a somewhat self-selected group from the poor and middle income population. Most wouldn't have joined if they didn't see it as a way out of a dead end life, but the patriotism stuff tends to be a secondary reason, indeed it's what distinguishes them from their peers who don't enlist.
I think that once they're in and have been through boot camp, then yes, I agree, they have bought in to the lore. By the way, I'm not saying that all of them have disowned that macho bullshit. It definitely plays into some enlistments.
The recruiters talk an excellent game: opportunity, training, free school, etc. Money.
