I'd say I see a disgusting attitude to "younger mother's" ( under 30 in Mumsnet land), and older mother's , ( gave birth over 40).
Women who have children over 40 , ( and normally the op is pregnant at 42 rather than 52, because, biology !!) are considered to "ruining their freedom" and "selfish as they won't be around to see their children grow up " ( ignoring the fact they will probably be 60 and working full time when the child turns 18, rather than 90 and needing a carer!)
The attitude on Mumsnet seems to be that if you weren't lucky enough to find your life partner young, you selflessly embrace childlessness cos having a child age 38-44 is the most disgusting and selfish thing. IRL , most people acknowledge fertility declines with age , but are happy if a friend / colleague aquantance is able to conceive in their late 30's/ early 40's. On Mumsnet people are "horrified" by the idea.
More seriously, the abuse on Mumsnet towards younger mum's is horrible. There was a very sad thread recently where the OP was 24 , had a six year old and a newborn , ( she was 3 weeks postpartum). She'd also lost a previous pregnancy at 17 weeks , and had clearly found this to be very traumatic.
At three weeks postpartum, she was typing about how appallingly the baby's father was treating her. Mumsnetters were falling over themselves to rudely demand why she'd had a baby so young ( at 24....) and tell her that "3 pregnancies by 24 was disgusting."
The same in the thread about the 19 year old who's health visitor was behaving innapropriately. People falling over to tell her that at 19 she wouldn't be able to parent without significant support.
The latter MNHQ needs to crackdown on, as young mum's won't post if they're asked to justify why they had a baby young.