I'll say though, those who think it will be better out almost always get out when they can. The limitation of those so disenchanted with the Corps they think using the GI Bill or doing some other work will be better is the end of their current contract. It provides a sure out. You have to actively convince yourself it doesn't suck enough to be trapped another 2-6 years, while other jobs you need to take an active role in leaving. Those who stay in think the Corps is worth it.
I've been in a couple industries and never seen the same. People hate their job/occupation field/company, and stay in it for a million reasons. The military is nicely set up to spit out those who won't buy into the institution.
I would be curious to compare percentages within military and police forces of those who agree that "life would be better out, but I don't have a better opportunity out". I'd put money on that subsection of the population being much lower for military than police (and most to all other industries really).