There is a high divorce rate, but I wouldn't put my relationship with my parents over my relationship with my husband. That would CAUSE a divorce. Actually...it would be a little disturbing. I mean seriously.
He is absolutely right to support the woman that he plans to spend the rest of his life with. A lack of commitment would cause a significant rift in their relationship. Would you rather have him not defend her? Come on, mom's a big girl, and she seems quite capable of defending herself. She being kinda nasty actually (no excuse for retaliation) but I would never want someone like that around my children.
My father has a temper, not that he is violent, but he raises his voice and will occasionally use profanity. My three year old son has anxiety, and is easily frightened. When he blew up in front of him, and scared the wits out of him. I took my father aside later, shaking with fury, and I told him, as calmly as I could, that if he ever did that again in front of my son, he was not allowed to be around my son. There were three months we didn't speak. While I love my father, my own family comes first, and it SHOULD come first. If either of my parents attacked my husband, I would defend him with the same fury. My husband should always know that he and our children come first, just like I know that we come first for him as well, every time, no doubt about it. It's how it should be. Hopefully THAT is the message they send to their children.
Their union isn't toxic, mom has made this situation toxic, (daughter in law retaliating hasn't helped in the slightest, but she's young) but, mom is older, SHOULD be wiser, and should be acting more like an adult. She should back off and try a different approach. It IS the bride's day, and of COURSE she isn't going to want someone who obviously doesn' like her, to be involved in her wedding.
Mom needs to suck it up, apologize sincerely, back off , and keep her head down. The problem is, she's not sorry. She feels all kinds of righteous, and her family is FEEDING it!!! Seriously...mom needs to grow up.