I mean, they have to have some kind of a basis for believing that "rapist" is the natural "untrained" male state of being, because that's pretty much what they're expressing... but the implication of that carries what I'd think would feel to a rational person like intellectual splashback.
You'd expect a person to be shocked when confronted with the notion that behavior he finds abhorrent is not just common to his sex, but supposedly universal. You'd expect denial, especially from someone without any tendency to exhibit the behavior. A non-rapey man should be appalled at being told that all men are potential rapists, and he should be offended and outraged at having that label applied to him. He should feel like he's been lied about.
For a guy to simply stand by and accept the label, or worse, participate in the application of it to other men indicates something about him... yet male feminists as a group do exactly that.
Here you have a bunch of guys supporting advocacy that says all guys are predisposed to rape unless taught otherwise.
That has to include themselves, doesn't it?
Is the reason they support the idea is because they think all other men... are just like them?