Studying people and their social behavior is indeed more difficult than studying objects, but attempting to do it scientifically is better than just theorising about it, especially when you then base social policy like "50-50 or it's discrimination" on those theoretical assumptions.

And the physical sciences keep finding out their previous findings were wrong, and readjusting, too.

The current state of knowledge is that the jury is still out on a lot of things, and much of the data on both sides of the issue is debatable, so neither side should feel too confident, but clearly both nurture and nature play a role.