this is kind of ridiculous. do you realize how broad a term “disability” is?

Well op didnt define it but i would assume everyone draws the line at a different place for the purposes of this thought experiment.

are they bad people for having kids when they knew we would inherit that?

Thats something between ur parents and god (and by god i dont literaly mean i god i mean whatever morality or personal philosophy they hold themselves to).

If u want/can go ask them what they think about the idea i recon it would be interesting to hear.