Why do parents do this?

What choice do they really have? Kill him?

The only 'choice' is abortion but unless it's inbred then they have no idea of knowing he'd turn out like this. No parent would ever bring themselves to kill their baby no matter how disfigured it might be,
True, but, theres a moment you realize its time to let to go you know, but i dont mean for them to kill their kid, but just letting him rest, but i guess you could try to say their enjoying the moment they still have with their kid, which is fair, i understand, but theres going to be a time, wheres having to take care of him will take too much time, money and effort, where he'll probably stay in a hospital bed waiting for his time to come, while his parents give him as much time he has left (excuse me if i sound sadistic, these past days have got me pondering my whole existance)