Assuming some day we will be able to fix genetic defects at the DNA level, the anti-eugenics crowd will be very loud. I don't think having ALS in our gene pool is a plus. The fact that we can keep people that have it like Hawking alive is a plus. But we and he would be much better off if he didn't have it.
I would guess that within 50 years we will have genetic treatments for defects like ALS. It may be a bit longer before we twiddle with the germline.
Opposition is already lined up. What happens if there turns out to be a simple childhood injection that boosts intelligence or athletic ability?