Not read the full thread or its predecessor as I don't have time, but my experience, for what it's worth....
Overall i quite liked mumsnet back when I bothered with it. If you go in the right forums there is excellent solidarity and advice during pregnancy and I got some great reassurance when I had to go and be induced. There are also some genuinely funny posters on there. I do remember crying with laughter at one thread about what's the most ridiculous thing your toddler has ever had a tantrum about (honestly some of the answers were first rate, particularly the woman who described pulling her toddler home after she wouldn't let him jump in a stagnant pond who described him aa hanging off her arm flailing "like a monkey on acid"). I do get how the relentless middle class-ness of it can get annoying though.
For me the most annoying thing was/is the militant parents of ASD/LD children, who insist on jumping on every single post where someone complains about someone else's badly behaved children being badly behaved in a public place, with the parents doing nothing about it , and hijack it to say "but what if the child has special needs!" and somehow turn it into an attack on the original poster for being intolerant of non NT children. Honestly some of them manage to do it even where there are no signs whatsoever that the kid in question is ASD/non NT and where it is quite obvious from the original post that the issue was the parenting (or lack of), not the child! It's like some of them can't accept that sometimes kids are just badly behaved and soft parenting is the problem...