I think eugenics, in principle, would be possible for humans--we routinely do it to other mammals... BUT ethical concerns aside, the selection for whatever physical or cognitive traits decided on would take so long (at least hundreds of years) that by the point it begins to take statistical effect society would already have changed its standards many times over, or blown itself up.
As for helping the weak, the 20th century philosopher Karl Popper had this relevant remark during World War 2:
"The theory that the human race might live a little longer if it had not made the fatal mistake of helping the weak is most questionable; but even if it were true—is mere length of survival of the race really all we want? Or is the almost perfect man-beast so eminently valuable that we should prefer a prolongation of his existence to our experiment of helping the weak?"
Strong people, in other words, can often be ass-holes. I've met plenty of kind people who are developmentally challenged, and many quick-witted bastards.
In any case, it's not like we're living in anything like a "natural human environment", as others have noted.