"Mentally ill" is today's catch-all phrase for dissenting viewpoints, that and "conspiracy". A way to delegitimize otherwise useful and valid viewpoints.
"They can't be right about flight. They're crazy."
"She wasn't raped, she's crazy."
"They can't really want rights. They're crazy."
"Medicine men can't heal. They're possessed by the Devil."
It's all the same argument with a different flavor. Side A doesn't like what side B has to say, so A says B has something wrong with them, and convinces C to lock them up and/or kill them.
It's dreadfully repetitive, and smacks of a brand of stupidity commonly called dogma.
The real fact of the matter is that mental "illness" is only an illness if it genuinely makes the victim's or someone else's life harder without outside interference (making your delicate sensibilities feel infringed doesn't count). Otherwise it's just a different viewpoint; nothing more or less.
The very fact that you can't seem to get over that and go on to make wacked out slippery slopes by combining otherwise unrelated shit instead of actually accepting that other people exist and moving on with your life actually speaks of a mental defect of your own.