I think it's so big now, posters don't really know each other and aren't able to make allowances when they know someone has had a shit time recently or their bark is worse than their bite, or they have a hair trigger on x subject but are brilliant on y subject. Eg I absolutely loved Franny but there was one topic (can't remember what it was now - something to do with child development?) which she would just always take incredibly seriously and be prepared to have an argument on. But you knew that about her so you didn't take it personal like.
I think you still get some of that here but only in the specialist boards or long-running threads. In chat or AIBU it's just sort of contextless mayhem and not much benefit of the doubt, meaning people are more likely to decide they've been mortally offended by something or other, so MNHQ are constantly being asked to sort it out which must be huge fun