I still think both Barb and Bob's plan was to keep Chris as close as possible, given both of them had offspring that didn't want anything to do with either parent, yet, at least in Bob's case, went on to be extremely successful and live stable, normal lives. There was that time early one when Chris wanted to go to an Anime convention (I think) and Barb throwing a fit, and Bob explaining that they were a single unit, and if one of the components leaves, the rest of the unit just fails.
Bob's plan seemed to be to get Chris through school, into some post high school education, and hopefully into a stable job where he could take care of both parents when they got old. Once Chris showed his true colors in college, and after, at Wendys, Bob had to figure out something. Getting Chris to be more independent would mean there would always be a fear that Chris would find something better and leave them, and why wouldn't he? Their other kids did. So Chris was groomed into believing that if he ever left, his parents would whither and die.
I guess his parents were right. Since the jail adventure began, Chris pretty much didn't care about Barb anymore, at least after a few months. The mortgage whining was mostly for his sake in getting the house, rather than Barb's, as we found out last spring. These days, Chris doesn't even consider Barb his real mother anymore now that he's in his new life. Still, both of them got more out of Chris when he was at home than they would have if he had just fucked off somewhere.
Not teaching Chris to be so gullible would probably have backfired on his parents, because instead of throwing some end of the world type rational, or feigning suicide, in order to get Chris to stop doing something, Chris could have seen right through those manipulations had he been a little smarter. Though after his last stint in the nut house, he seems to have understood Barb being manipulating and abusive, so there's some validity to his parents not wanting him any more street smart.