It's irrelevant if good and evil are social constructs or not. What is relevant is that these constructs are vital for civilization and without them civilization cannot exist. Relativism leads to a lot of people doing a lot of harmful things, especially among people with great power, as we see today (pizzagate, satanism, i.e.). Absolute morality are very important and evolutionary beneficial constructs.
Again. Unfounded claim.
Hitler was an absolutist. Same applies to every major leader that ever lived. They butchered millions.
I am not saying that relativists don't commit crimes but , come on. Be a bit intellectually honest here.