Although they claim to be the party of science, the left thoroughly believes in many unscientific things. They refuse to acknowledge human nature and the natural differences between the sexes. They don't even believe in there being just two sexes.
There are other human differences they refuse to see, but those are the biggest.
They think humans can be constructed by a diagram, and only they have the master plan. Incredible misery has been inflicted on multi millions of people by leftists who wanted to remake the world in their image.