Did you note the word "usually"?
Yes.
I know that you said,
"The word "evolutionist" is usually used as an epithet implying an unreasonable belief in evolution."
And I was surprised to hear that the word "evolutionist" was ever used as an epithet, (Unless the person saying "evolutionist" spat out the word or did something equally offensive.)
Evolutionist seems like a fine word, to me. And it seems fine to the NIH.
Is there another short1 word that I should use?
1 I'm usually strapped for time.