Being an incel is a choice

It's short for "involuntarily celibate", though.

Although I guess identifying with those words is the choice you're talking about

aren’t mentally ill. The most generous descriptors I could give them is that they’re either misguided, brainwashed, or both.

I'd argue that their brains are at a state of did-order, be that due to someone having pushed propaganda on them or not.

Some people are less capable of being critical of their own thoughts. For example, young children are very impressionable. Lots of people grow out of it. Lots of people don't.

If I harassed you with say, targeted ads and some videos I made on YouTube, it could definitely make you stressed out, thus me having affected your mental health.

Now being a racist because you grew up in a small racist/sexist/homophobic town or something might not be the exact same thing, but the point I'm trying to make is that their wrong choices — like "choosing" (I use quotations because it's not exactly a conscious choice people make, although displaying those attitudes definitely is) to be racist or transphobic or whichever kind of bigot — are a symptom of the disorder they're having.

That disorder usually being amathia, willfull ignorance.