How do I explain to a person that the "red pill mentality" is stupid?

This also presumes that aspects of the root cause are changeable. I grew up with a guy who became an incel in the pure sense, not political sense.

The poor guy was hit with the ugly stick very badly, and then had an accident that left him partially disabled.

When puberty hit and everyone became horny assholes, he had a double whammy of being a horny asshole too, but getting ignored (at best) or out-right derision from the teen girls he expressed interest in. He was also self-aware enough to both know that he was a hypocrite because he only wanted to date an attractive woman, and that he understood that goes both ways (societally and biologically) so he went into a cycle of vocal self-loathing.

You can guess the rest. Those behaviors compounded and altered his personality to the point he was no longer the happy go lucky ugly ass dude and was now the guy who was just as ugly on the inside as the outside and no one wanted to be around that negativity.

I have no idea what happened to him after college as I never went back to my HS town after my parents moved away from it. I would like to think he is doing better with age and therapy, but I doubt it.