It's a difficult situation. I feel like people who say BB is in the wrong haven't actually been in a situation in which their parents, or at least one of them, push so far that there is no option left than to go NC.
I also think if somebody then calls out their behaviour they usually focus on either the most recent harms or they choose not to address the most painful ones deliberately, it's just too much to deal with or they want to keep it private because of the hurt.
I understand it doesn't come across well in public. I also understand there must be a lot more to it and it is the final straw scenario.
I went NC with my father at the age of 32 after a lifetime of horrendous, abusive behaviours of all sorts. I never regretted it. I rarely think about him. I hate the harm he caused to his entire family. My relationship with my DM has suffered massively too as she remains married to him and it's really heartbreaking. I kept that private apart from closest friends because I felt embarrassed.
OTOH, my DH was/is in BB's type situation. Narcissistic, lying MIL, running the whole family like a dictator. Ruined his previous relationships, tried to ruin our wedding and did not succeed. Things that he told me since about her and his childhood and what I observed independently confirm without a doubt she is vile and toxic and it is best to stay away. We both called her out many years ago around the time of our wedding and much in the same way as now, it was controversial for some, we were judged and criticised even though everything was factual and truthful. People were either too scared of her or didn't want to get involved. But the issue with that is, it condones abusive behaviour and many people suffer as a result, usually those younger and inexperienced. It's not OK to shut your eyes and enjoy your questionable moral standing for an easy life if this kind of stuff is going on within your family.
I think the difficult thing is this is an often lonely place to be and it is true to say bridges will be burned if him and Nicola ever split up. However, he has to live his life now and he chose his own ethics and peace, he spoke up and he stands by his own rules. I think this is to be respected.