The same way JB and Michelle have, by thinking their methods work despite all evidence to the contrary, ignoring red flags (because there's no way there weren't a lot of them), and forgiving him over and over again. I'm not saying they're completely responsible for his behavior, but I do think their constant, unconditional support gave him some cover. Forgiveness=Permission in a lot of cases.
I know the popular theme around here are that people who grew up fundie are "brainwashed" and don't know any better, but this generation is pretty plugged in to the rest of the world. And they've pro