So, the lady, who has to have maximum shields up to deter the narcissists, blast the nice guy right out of the water. Well, the nice guy won't be doing that for a while... if ever again.

Oh yes, 100%. It's scary, because it's a lose-lose here. And I see a lot of women saying woe to the nice guy for not trying harder, but idk, put myself in his shoes, I probably wouldn't want to be that guy, either.

There is no reason left for a good man to marry a woman.

I don't share that view, though. I think men are making many mistakes, too, and I try to keep a centre POV. I don't think either sex is completely blameless in what's going on out there. Though I do agree the system is skewed towards the women, especially when it comes to custody or divorce agreements.

He does get her cruelty.

Men can be cruel, too, though. Even nice men.It's important to remember that, in everyone's interest, really. It just is, as it's always been, a two-ended job. If we want this mating business to work for everyone, we gotta both put in the work, I feel.

And he is not guaranteed sex, not even on the wedding night.

It seems to me there should be no wedding night in that particular case. If one party has such little interest in sex, to begin with, why be in a relationship at all? But I think it's a mismatch, rather than a case of if I, Nice Guy, were to marry a woman, she'd be just as likely as any other woman to withhold sex (on the wedding night or any other). I don't think that is the case.

And lonely young men, with no future prospects are the most dangerous creatures on the planet.

100%. We live in very dangerous times. I think the whole generation is purposeless and that's making us extremely volatile. Having no purpose makes it much easier to latch to a cause, in the quest for identity. For meaning. No one has meaning, and with the rise of AI, now, we're about to have even less.

The average (80%) men are walking away.

I think that's a mistake. I used to write this sort of opinion piece over on Medium (got accused regularly of supporting the patriarchy or whatnot), but I also interacted with a lot of proponents of the men going it alone movement, or whatever it's called.
That's not healthy, and that's not adaptive. Because when a nice, young man decides I'm not gonna bother anymore, he's not reacting to an aggressor (e.g. a manipulative woman), but to an idea. That's not how you heal from trauma, neither as an individual, nor as a society.
I don't think it'd be okay for me, as a woman, to say oh I had a negative interaction with a man, I'll swear off men. So I don't think men should do that, either.