They need Darwinism to be true because it is the "disillusioned Christian atheists" creation myth...the only way they, as disbelievers in God, can explain why we are here is that it is an accident (random).
One of the prophets, Richard Dawkins, said, "Darwin made it possible to be an intellectually fulfilled atheist."
This is why there is panic among these disillusioned dudes whenever someone (like me) mentions the scientific criticisms or vast evidence against evolution.
The real reason evolution became an issue in the general public is because the theory of natural selection was being used to justify racialist theories/policies and eugenics. In fact, the "expert witnesses" in the Scopes trial, the ACLU inspired publicity stunt, were all champions of forced eugenics.