Darwinian evolution is, after all, the one ordering principle in nature whose origin and mechanism we seem close to understanding fully. It must, they feel, explain everything. Just So stories. A theory that explains everything might just as well be discarded since it plainly has no real explanatory value. Of course, the other thing about evolution is that anything can be said because very little can be disproved.
Experimental evidence is minimal.
The same might be said of genetics, though here, I acknowledge, there is a more solid experimental foundation. But in both cases the open-endedness of what can be said has led many biologists into the realm of pop Darwinism and pop genetics. We saw headlines about the gene for homosexuality, only to discover later that it wasn't a gene and, in any case, the correlation was very weak. We see further headlines about the Darwinian basis of the sex roles or almost any other set of human behaviours you care to name, only to discover that the arguments are based on very long and patently unsustainable chains of historic causality. And, anyway, they cannot prove that culture and environment did not play an equal or more important part.