Why dont these guys go gay? And then when they look at each other they would understand why nobody else will sleep with them either. It should work, and give them some perspective.
Sometimes, incels outline absolute bat-shit crazy plans like this, and they will usually include a part that says something to the effect of "And this will benefit women too, because blah blah blah".
One that actually would benefit women is if fewer men were born. Not like, "kill all men" or harm men who are alive today, but just do what China did, in reverse. Men are born at a higher rate so it wouldnt actually skew the numbers the way it did in China. You would have a much lower chance of running into dudes like these guys.
I actually dont really see any downsides to such an admittedly bat-shit insane plan. Automation will replace a lot of the work that men traditionally did, and women are generally more successful and valued, productive members of society. Not every man is going to go on to be Elon Musk, a supergenius being held back by having to work in a factory--most of them will melt down. Look at all the men who voted for Trump because they were afraid of an economic collapse, and everybody was telling them he's not gonna fix it, and they're right, but these guys still voted for him because the writing is on the wall.
And you could just share the men worth sharing. I've read some tumblr-esque things suggesting that monogamy is actually very slowly fading out, so it's kind of a natural evolution.
Overall though, the true irony of it for incels, would be that, still, even if one of these dudes was the literal last man on Earth, women still wouldnt fuck him.
