You don't understand how crushing having a severely disabled child can be to a parent. Not only do you miss out on 90% of the joys that come from being a parent unless you are very wealthy it condemns you to a life of being a carer 24/7 and your whole life having to orbit your child. Not only that it gets worse as time goes on, instead of your child supporting you in your old age you have to instead support them even as your body begins to fail and you need help yourself. This gets magnified when the child has aggression and emotional problems and your health becomes endangered by them whilst you also lose the ability to physically discipline them.
So overall it isolates and enslaves you.
The solution is either to have humane homes for these kind of people or a publicly funded carers or nurses who can share the huge burden with parents.
t. Guy whose friends mother had a profoundly autistic son.