I have a nephew who has significant SEN. It's extremely unlikely that he will ever be able to live independently. My sister and BIL spend a considerable amount of time planning - and worrying - about what will happen to him, and who will look after him, when they've gone.
Your blithe little statement "we have a welfare state" demonstrates a profound ignorance of the availability of state-backed help in this day and age - and under this current government. Social services and community care has been completely eviscerated. You have to be absolutely desperate and on the complete bones of your arse before the state will step in. And even then the "welfare" is in many cases not even enough to live to the most basic of standards. There are genuinely people who have to choose between heating and eating.
The state provides zero respite and support for my nephew - it was a local charity that did that. Guess what - they've just closed down because of lack of funding and because the rent on their building doubled. The local council declined to offer any support, so now 100s of families that were being supported now have no help at all. To suggest that those families should decide not to leave any provision for their children is fucking laughable. Who is going to look after them when their parents are gone? Do you have any idea of how poorly mental health and SEN provision is for adults right now? It's bad enough when you're a child because CAHMS is stretched to breaking point, but once you reach 18 - forget it, game over.
So you can take your egalitarian ideals and fucking shove them, quite frankly. But what do the disabled matter, eh? We have a welfare state!