It's morally wrong to say they shouldn't be able to reproduce, they are humans just like each and every one of us. The thing is, being disabled does make you inferior, not inferior in sense of power, but inferior as a human(In relation to the rest of our race).
We set ourselves apart from any other living organism due to our potential, take that away and we're.. useless & that's what a rationalist/realist would say. It's hardcoded in our functionalist mind to do whatever we do to ensure survival and growth as a race so if someone doesn't think they should reproduce, fine by them, it's their opinion and I greatly respect it.
However i've met many disabled kids (-/+ my age) who have been.. so kind hearted, genuine people who treat you with love to the point where it makes you question, 'What is the human race without it's purest essence, love?'
Any human or other race that emits the feeling of love should reproduce, in the end of the day that's the only pure thing we've got left in this cold world.. there's a famous saying my mother would say about my father and most of the men in this world and it's a saying I never forget..
'A man with two brains has only half a heart, a man with half a heart is left only with half a soul.'