Disney is no different than any other large conglomerate out there. There are many, many levels of pay for many, many different types of jobs. The majority of the people who work at WDW are more than able to afford their mortgage and their car payment, along with saving for their kids' college funds and taking a vacation every once in a while. If affordable living wasn't possible on Disney salaries, no one would be working there.
As for "the amount of forced cheeriness they have to display and the enthusiasm that they must empart," I've found that the vast majority of CMs do that naturally, and would whether they were at Disney or anywhere else. Disney doesn't "take advantage" of anyone. The people who choose to work there are grown-ups. They're able to weigh and offer and see if it's worth their while. If it's not, they have lots of other places they can go for jobs.