Same here. I planned for all my children to be able to go to school, not for one of them to be in intensive care once every 3 months for weeks at a time, and then at home recuperating. Perhaps I was foolish and all family planning should take into account the absolute unthinkable.
I believe Carers Allowance, or Invalid Care Allowance as it was first called when it was introduced in 1976, relied on two things:
Firstly, at that time disability was characterised by the medical model, and a huge percentage of physical disabilities were either the result of service during WW2 or industrial accidents. Ex-servicemen received other benefits, industrial accidents received compensation. With an average male life expectancy in the UK in 1976 of 72 years, Invalid Care Allowance was seen as a 'stop gap' or a 'top up'.
Secondly, institutionalisation - those with learning difficulties or mental health issues were routinely segregated from the general population and had limited access to education and / or employment. Put bluntly, they didn't need as much support as they were being effectively warehoused.
In other words, there was no expectation, in 1976, that what would evolve into Carers Allowance would be replacing statutory services or benefits. Over a period of years, since the mid-80s, successive governments have outsourced what should be formal care (i.e. provided by the NHS or Social Services) into informal arrangements (i.e. so provided by families). This has saved our welfare system £billions at the expense of some individuals. I do believe this represents a significant case for discrimination.
I can see some arguing the case in terms of disabled children. It should be noted in the case of children that the state are responsible for providing education and, where possible, that means those children are at school for 6 hours a day, 5 days a week, 39 weeks of the year. Yes, under those terms, the 'top up' can appear reasonable. Where it falls apart is when the children aren't at school (see above re: intensive care) or where we're dealing with an adult / not a child. Providing evening / school holiday care is dramatically different to providing 24/7 365 care. However, there seems to be no distinction in law / benefit.
As I say, I don't believe there is, or ever has been, any sort of proper conversation around the impact of this.