I'm willing to accept that descriptive statements may be necessary in deciding moral action if you're willing to admit that descriptive statements are not sufficient for deciding moral action. I'm not even sure they are necessary but it's also secondary to the primary point of contention.

I didn't say pain in others does not compel me to act. I said the mere description of pain in others does not compel me to act. I am only compelled to act when I decide that I should. Whether that is to placate the uncomfortable feeling of watching someone suffer or simply because I believe it is right, nothing intrinsic to the description itself prescribes a course of action.

Your (descriptive) pain does nothing to spur action in me. Of course, my own pain spurs my own action, but I can find no prescriptive reason it should. In fact, the compelling reason to act on my own pain is involuntary. Morality is a question of who we are/how we act precisely when we are given a choice.

> Science cannot provide justification for the value clause". Why is this necessary? Isn't the justification simply that we want a better world as opposed from a worse one?

No. That is not the justification. That introduces the concept of "better" before it has been agreed upon.

The justification needs to explain how science, which provides a descriptive explanation of how morality evolved in human beings, entails a prescriptive statement of how humans ought to be. Morality is not simple stating truths, it's imperative. Something must appeal to action.

Is/ought is relevant because, sure, morality as described as a human phenomenon aims at protecting certain evolved desires, but science can't prescribe morality. It can't tell us whether or not we should have those desires.