I agree with this. It's one of many factors though.
House prices are one factor - it's seen as undesirable today to be a sahm (see all the threads about 'you need your own financial independence). With both parents working, children don't have the full attention of a parent for much of the day.
SEN needs are not adequately catered for. It's fine to try and integrate all children in one system, but it's not working because of the lack of resources.
Parents (some, not all obviously), do not discipline their children adequately. (See all the threads about 'my three year old hits / scratches me). I'm elderly now, but if one of my toddlers had hit me, the result would have been a smacked bottom. That's another thing that's hugely frowned upon now, but it may change in the future.
The world is arguably more dangerous today. Children can't play out on their own, partly because of parents' fears of predators, and partly because of the sheer volume of traffic. (Again, house prices mean that 2 salaries are needed, which often means two cars per household).
Children very rarely sort out their own disputes - they are always with an adult who intervenes, and this leads to a diminishing sense of independence.
I think we are close to tipping point with schools. Teachers are leaving in droves.