Would I encourage my partner to abort in those cases? Probably. Am I comfortable telling others to abort their kids? No. Making that law? I'd be crucified for it. It's specifically a dodge because there's a discrepancy between what I would choose and what I think society as a whole should choose.
My bioethics professor always encouraged us to use a particular thought experiment when we were facing an ethical problem. He said to ask the question universally, usually phrased as 'What would society look like if everyone made the same choice?' Now, for that question to have any meaning in the context of our discussion we would have to go disease by disease to ascertain the 'rightness' or 'wrongness' of preventing pregnancies in given situations. For most of the ones I listed however, I think that those embryos should never, in any case or situation be implanted and/or carried to term. (I'm separating conception and pregnancy here, assuming technical limitations requiring/allowing these decisions to be made.)
I still don't think you can say that everyone with every one of those diseases would be better off not being born for them. Some are treatable, some may one day be curable. Cystic fibrosis used to be a death sentence, but recent drugs can completely fix certain mutations. Still, in the constrained case of uncurable, developmental defects that lead to a short lifetime of pain, followed by death, I would agree. But that's a bit more limited than what you're saying. Appreciate the discussion.