@ Pharaoh Bastethotep:
I think there are a few main types of "incels":
Young guys who think high school is real life and that they'll be bullied forever over traits (such as bookishness) that most people grow to admire or at least to ignore.
This set kind of includes even the 27-year-old quoted by an OP here. He might 'just' be socially awkward without having found a way through that stage yet, and would benefit from counselling by a trained sexual surrogate (if there is one close enough) or by a licensed therapist who specialises in social anxiety. (Too bad he went to a fetid shitpile of fuckheads instead of virtually anywhere else on the internet.)
Older guys who either forgot or never learned that a good marriage takes two people acting in each others' best interests, rather than one asshat constantly whining because his wife had "lady friends" who implanted man-hating ideas into her otherwise empty head, else she'd not have concluded their marriage was a shit sandwich and ended it herself. The breakup was all her fault, all her mother's fault, and all her female coworkers' and friends' faults. She took him to the cleaners. He was a nice guy 'til the bitch ruined his life. Yada yada. (There are crappy women out there, but I doubt most of those rabid old incels were the victims of such women as opposed to being victims of their own stupidity.)
There are additional men, old and young, who've never been in a long-term relationship because they give off major 'creeper' vibes. These guys can usually be told apart from average late bloomers' by the fact they're not really “friend-zoned” so much as avoided outright. They seem to think the world is at fault for their lack of fulfilment and that someone (or all women, or “Chads,” etc. etc. etc.) should be punished horribly; raped, mutilated, killed and so on.
The latter groups are plain poison to average men who want fulfilling long-term relationships but haven't found them yet.
The natural population ratio of male to female is about 1:1. That means for nearly every man alive, there is probably a woman who shares his interests, his temperament, and many of his goals. It might take longer for some genuinely nice guys to find mates if they're not considered conventional - conventionally attractive with conventional interests. Girls, like guys, take time to mature. Eventually, and I honestly believe this, most people alone into their 20s or 30s will find someone who is a good match. By that age, all the weird teenaged angst has usually burned off and things important to people in later life become more plain to younger people looking for lasting partnerships. Other things, like looks, become less important. Women beyond a certain age will often start choosing mates from among men they once "friend-zoned" in part because superficiality starts disintegrating in the face of time. They know looks will fade. They want qualities with a hell of a lot more longevity. Beyond that, they've often known these friends long enough to feel more assured of their own safety in dating and marriage.