The naturalistic fallacy is that you claim something is good just because it's natural.

Both Red Pillers and Blue Pillers fall for this all the time.

For example, if I say that I believe men are natural rapists under certain circumstances, does it mean I am saying it's a good thing? Does it mean I am making any moral judgement? No, it's just an opinion about male nature.

If I say that I believe men have ephebophilic tendencies does it mean I am saying it's a "good" thing? No.

The whole civilization is literally about suppressing our base, animalistic desires. Natural=/=good.