I've read some horror stories from parents and siblings of disabled children and it's genuinely sad.
The siblings are unhappy because they're overlooked and don't get their emotional needs met. They're just another caregiver for the disabled child.
The parents have to focus all their energy and resources on a child who'll never grow up properly. They won't see it hit the usual milestones of life. They won't see it have children. Their bloodline likely extinguished
One particular case that stuck with me was a mother caring for severely retarded kid who was mentally a 1yo but physically above average.
By fifteen he was a strong young man, but constantly in need of supervision, constant violent emotional fits, the mother was often getting punched in the face while trying to change his diapers. She had to dedicate every second of her life to taking care of that kid. She had to be unemployed because of this and the care was expensive
There was also the option of putting him on medication, which basically made him a vegetable.
What's the point of letting kids like this get born? They'll never contribute anything to society. They'll be a drain on their family and society. They'll make life miserable for their family. And they'll never be able to even experience life like a normal person