Personally, I wouldn't want to breed under those conditions, but I don't think it's immoral for someone else to go through with it - who am I to put a value on their relationship with their (potential) kid, or to put a value on that kid's life. I've met enough happy/productive people with developmental disabilities and/or health problems to say "Yeah, not worth it in any possible situation" for everyone, everywhere.
Apostheum said:
The point is that this child would SUFFER. As in, every waking moment would be in agony. Combined with further mental trauma due to the fact that this child cannot interact with other humans in a meaningful way, and (if the mental impairment isn't severe enough) will realize it will never have a girlfriend/boyfriend or play with other children, ON TOP of the despair in knowing that it will continue suffering like this until it dies a premature death.
The OP didn't specify that the kid would be in pain, so where are you getting this life of constant agony? "Health problems" can mean any number of things - not all chronic health conditions are painful. And I've certainly seen developmentally disabled kids playing, so what's that about?