All parenting is hard and frustrating though. The whole "caring for a disabled kid is so hard!" thing just ends up getting used to excuse child abuse when it's directed at disabled kids. Ask me how I know.
Personally I'd probably end up sticking any baby I was the sole caregiver of in a blender, disabled or not. That's why I'm never having kids. I think a lot more people than would openly admit are the same way, and a lot of "special needs mamas" who treat their kids like shit probably would abuse and resent any kid they got stuck with (and are just using the kids disabilities as an excuse).
See also: Robyn, who blatantly favors her immobile, largely silent potato over her healthy kid.
I understand that parenting in general is difficult, and as I said, there is never, ever an excuse for hitting a defenseless child. I'm sorry that you have firsthand experience with this, too.
However, I think it's negligent to pretend that parenting a healthy, normal child is just as difficult as parenting one with significant disabilities. Yes, a parent's responsibility never truly ends, even when a healthy child reaches adulthood, but as the kid gets older, the nature of that responsibility evolves. Children get older and become more and more independent. During those really hard days, there's comfort in the knowledge that it won't last forever. There's a saying, "the days are long, but the years are short". Kids grow up and need less parenting, particularly less of the "hands-on" dirty work.
With a severely disabled child, though, there's no respite in sight. He will depend on a parent or caregiver for every need, forever. There is the constant expense and hassle of getting necessary equipment and supplies. There's the physical labor of lifting, moving, washing, dressing an adult-sized person who cannot assist at all. There are trips to specialist doctors, many of them. Sometimes, there are hospitalizations which cost thousands - hundreds of thousands - of dollars. Parents of special needs kids, whatever the level of their disability, will almost certainly watch their child suffer, whether it's watching their autist be left out on the playground, explaining to their son with DS that he will never be a dad, or watching their spud die of a respiratory infection after years of deteriorating from an undiagnosed genetic condition. The parent will never pack him up in his car and watch him drive off to start his independent life. The thankless drudgery of having a small infant never ends, but it may be even worse because he might not even recognize his parents or show affection. The milestones everyone else gets to take for granted come late if they come at all. The parent is exhausted, tired to the bone, but doesn't get a moment of rest unless the child dies or is institutionalized. This is even more true for parents of children with degenerative conditions, who are forced to watch their children become
more dependent with age rather than less.
It's not an excuse to abuse your kid, but it has to be soul-crushing. Parenting a severely disabled child obviously has rewarding moments, but it's bullshit to pretend it's all smiling tards.