I am not in any way condoning any vitriol found in any posts, but I feel the need to point out celebgran that there is a fair amount coming from both sides here. Both sides of this argument have posters who choose to make inflammatory posts that attack the other side. I don't think I need to name names, we can all read. When a poster resorts to name calling and personal attacks and rhetorical questions that take a comment to its most absurd extremes, they are not gaining any credibility for the ideas they are presenting/defending. It's childish, really. It's the Internet equivalent of "I know you are, but what am I?" How about we all stop attacking each other and fuelling the fire.
I will say one thing about Araabra's "going along to get along" policy for keeping the peace. While I agree that it can be taken too far, and not speaking up for yourself will turn you into a doormat, and no one should feel they are "walking on eggshells" ... I think that's different than simply holding your tongue and not giving unsolicited advice. When it comes to unsolicited advice or matters that aren't actually your business, Araabra is right. Earlier on, someone else put it as "least said, soonest mended."
In my experience with my MIL, she wanted to give advice about every aspect of our lives, whether it was her business or not - and then she would get upset and argumentative if we chose not to take her advice. If she had been able to hold her tongue even some of the time, and wait to give advice ONLY if/when asked, we might not have felt the need to CO completely. The whole withholding of my baby incident only happened because I chose to take a medical professional's advice over her opinion, which of course was given unsolicited. She probably wouldn't have felt the need to do that if she had been able to accept that it was MY decision to make, not hers, and that even if I was in the wrong, it's also MY mistake to make. The same goes with all her comments about who was doing the cooking, rather than congratulating my husband for learning a new skill and being happy for him. If she had just kept those thoughts and others like them to herself, we might be in a completely different position.
That's really the critical difference between being considered "annoying/overbearing at times, but reasonable" and full on "toxic BSC." And yes, it applies to both sides. There are times that AC need to back off and let their parents run their own lives, but I think it's a harder adjustment for parents to defer to their AC In that way, because it feels like a role reversal. Really, it's just the natural order of things.
I also happen to agree that marital issues are best kept between those who are actually in the marriage. If a 3rd party needs to be brought in, it should be someone who is there to help both partners work things out themselves, not to advise only one side (and this would certainly not be a good place to go giving unsolicited advice to the other side). Unless you are concerned for your safety - then you may need the support of others outside the marriage, but at that point whether your marriage survives the breach of privacy is the least of your worries.