SE23.com does seem to be particularly critical of mothers. I have seen few threads that generate such ire as those where mothers and children are concerned.
Like CatfordBorders I have come across plenty of rude people and nice people in Forest Hill. I don't think there is a particular generation of lax parents / badly behaved children - it is just perceptions.
Talking of rudeness - people who talk on their mobile phones whilst being served in shops! That is so rude and I've come across plenty of those around here, it is impolite to the shop assistant, and holds everyone else up! There was a particular lady in Sainsburys who insisted on chatting on her phone whilst packing her shopping very slowly, causing a long delay. I was in the queue with my toddler who was getting more and more fractious the longer we waited, and no doubt someone behind me in the queue was tutting about why anyone would bring a child shopping anyway and why I didn't have a magic formula to keep her quiet....
The British do have a particular knack for the tut tut and disapproving look. On an airplane journey my husband and two children were unfortunately seated just behind such a couple and their teenage daughter. It was a midday flight, Easyjet, from Malaga, school holidays, so plenty of families on board. My children weren't being badly behaved, we had brought lots of magazines to occupy them, but they were chatting a lot, as children do. The family in front seemed to think it was a good time and place for a nap and kept giving my husband those 'looks' - the teenager in particular had her eye mask on and was sighing a lot. To me, that was rude behaviour. I was much more fortunate to be seated with my baby next to a young American man who couldn't have been kinder, asked if I needed anything, chatted to me like a normal person, and had a very pleasant journey.
Or the recent train journey where I was travelling with 3 children and had specifically booked seats so that I could sit with the children (they are too young to be sat on their own), but the older gentleman who had sat in our reserved seats and could see me struggling with kids and bags refused even to catch my eye when I said they were our seats and stared deliberately ahead. That was rude. But there was a lovely younger couple who moved out of their seats so that I could sit with the children. That was really nice.
People are nice, people are rude. C'est la vie. I don't think it's helpful to demonise a particular group of society.