AJM, I do agree with you about trying to encourage kids to get along with their parents, but MLCers can be very emotionally abusive, and it isn't necessarily healthy for anyone to have more than polite and limited contact with that.
I am not at all sure that my sons would go to their father's wedding should he take it into his head to marry one of his women friends. 'Should' they? Honestly I think it depends. I wouldn't object, and indeed it is not my place to mind (he would probably invite me too, as a matter of fact)
I have a good friend with an emotionally abusive mother. Reluctantly she has stopped all contact as it was too damaging to her. You do not have to be an axe murderer to be capable of harming others! Parents have obligations to respect their children and the children's feelings too.