I think this show has totally damaged their ability to actually grow as people and become functioning adults. The steady stream of MTV money gave them no reason to have ambition and try to better themselves (this is true of pretty much all the Teen Moms, of course, with the exception of Farrah who, for whatever else you can say about her, has always had hustle), and being on TV has given them a false sense of self-importance (again, this is true of pretty much all of them - when these shows finally come to a real, permanent end, I would be very interested in seeing a decade later "where are they now" to see how they coped without the show).
But even more than that, I think the experience of the show has psychologically damaged Cate and Tyler (particularly Cate) in ways that might never be undone. If 16 and Pregnant had just been a one-off show, I think that they would have been fine. They would still have had to find a way to break out of the cycles of drug addiction and poverty that their families were stuck in, but I think that they would have found a way (albeit maybe not together, and that might have been for the best).
But the show turning into an ongoing thing is probably the worst thing that could have happened to them. They put Carly up for adoption for a number of reasons, but one of them was certainly financial - they knew they couldn't provide for her in the way that she wanted her to be provided for. Yet here they are now with this MTV money, probably thinking that if they had known then what they know now (that the money truck was about to pull in) they wouldn't have gone the adoption route. I think at least some of their issues are a result of trying to grapple with the guilt and resentment and all the "what ifs" that flows from all that.