I think it's a bit of a mistake to make *any* "All men are thus" statement-or, "all women are thus", or "all humans are thus", other than things that are pretty much true by definition (like, for example, "all humans are mammals"). But, add in an "almost", and you're generally golden, as long as your generalizations legitimately are general. 'Cause, well, humans are complicated.

I suspect there are some people out there who really *are* wired for monogamy--who won't so much as be interested in another person when they have a partner. Such people may be rare, but I'm sure they *do* exist.

And there's a larger subset (still small, but larger) who refrain from specific actions, such as looking at pornography--from lack of interest, for religious reasons, because visual stimuli don't really turn them on, whatever.

This is not to say that I think girls have a right to expect that of their partners, barring prior freely given agreement--just like girls don't have a right to assume their bf's are among the small percentage of men who don't like blowjobs, or something like that. The existence of a small subset doesn't mean you get to assume people belong to that small subset because it's convenient to you...