Though thankfully, I'm not estranged from my AC and families, I know that "you never know" and so, I read threads about estrangement both here, on MN and elsewhere. As such, I have some opinions on the topic of this thread.
IMO, it's good for both AC/CIL and parents/PIL to realize there are "2 sides to every story" and get a chance to see what might be the other perspective. However, the 2 threads being discussed on MN, as I understand it, were opened up as support threads for EPs/EGPs. While sometimes one poster will make a suggestion of how another poster might handle their situation differently or question a choice they made, it's usually done gently, and for the most part, those threads are for people to give each other comfort. Some of the situations are, sadly, beyond hope and the GPs just need something to help them to get through and move on. Even if the scenario isn't hopeless, sometimes, IMO, a person needs to hear, "I understand." There's a place for constructive criticism, I believe, but not in those threads.
In fact, I've read threads on MN where I could see what the MIL's perspective might be and how the DIL might be missing that - and yet other MNers rallied around her to agree that her MIL was a terrible boundary-stomper and so forth. Sometimes a DIL/AC needs that kind of support and sometimes a MIL/parent/GP needs that, too.
Also, while I agree with those who say the MN thread is merely pointing out that there are 2 sides and so on, some of the posts say very cruel things about the EPs in the estrangement threads, even suggesting that the EPs feelings have no validity. IMO, while some EPs may be totally in the wrong, that doesn't mean that that their feelings aren't very real or that they don't actually have a side to the story.
Interestingly, if you (general) read carefully enough, you'll see that both sides tend to accuse each other of NPD! Not sure what to think of that...
Meanwhile, my heart goes out to all the DDs/DILs who have come in here and told us about their problems w/ their MILs and so one. Thank you for reminding us that AC/CIL can suffer, too. We need that perspective.