Rejecting science is, I think, the motive behind the crazy push to claim that gays can marry (laws notwithstanding, gays do not form the biological relationships that exist to produce and nurture children and thus cannot truly marry) or the claim that a man can become a woman just because he says he is a woman.
It is necessary to reject science in order to support abortion through all nine months of pregnancy. To support abortion so rabidly, one must either argue that the unborn is not alive—contradictory to scientific observation—or that the unborn has no right to life, which is a more difficult case to make. Furthermore, successfully convincing people that the unborn has no right to life leaves open the door to kill anyone who does not produce—handicapped, retired people, children.
Science tells us how the world works. Leftists can try to reject it, but they cannot change physics (the basis of all science).