Prescribing a behaviour is a problem for some because it forces them out of the world of determinism.
And some, just plain and simple, do not want to be disturbed in that comfortable and warm place.
It’s not obvious that many of our daily habits are better or worse than some of man-kind’s most egregious atrocities.
That is unless you want step outside of physics.
And what comfortable person wants to do that?
Morality, like numinous awe, is a jump; in it, man goes beyond anything that can be ‘given’ in the facts of experience. And it has one characteristic too remarkable to be ignored. The moralities accepted among men may differ—though not, at bottom, so widely as is often claimed—but they all agree in prescribing a behaviour which their adherents fail to practise. All men alike stand condemned, not by alien codes of ethics, but by their own, and all men therefore are conscious of guilt.