I remember reading about those forums, though I never dared go look at them. I did once see a bus ad for a local women’s shelter that had been graffitied by somebody enraged at feminism for encouraging their daughter-in-law to “steal” their grandkids from them and their son.

I also recall the journalist mentioning that yes, some people’s adult kids do suddenly break with them because they join a cult, have a controlling spouse, etc—but those parents, if they do join an estranged-parents’ forum, usually figure out pretty quickly that it’s not for them and go find a different forum that matches their situation.