Partly, I suspect that being attacked would ruin the mood for me, thus rendering the exercise futile.
Except that penises don't work that way. One of the main reason that men who are raped by men don't report is because they're confused or embarrassed because they got an erection or even ejaculated. I mean, if you could just turn it off with willpower, why would premature ejaculation ever be a thing? Why would teenagers have to carry things in front of themselves on occasion?
But okay, just because I find it difficult to imagine doesn't mean it doesn't happen.
And we're better off with people who disagree but have open minds and are willing to listen than with people who all mindlessly agree. I tip my hat to you, sir.
if she's attractive, why does she feel the need to force anyone to have sex with her
You girlfriend wants to get pregnant and you're not ready yet, your ex wants to get back at you, she's mad at your girlfriend, she's mad that you turned her down - sexual assault it isn't usually just about sex, it's sex and power.
bigger and stronger than me enough that she could overpower me
What if you're sick or injured or drunk or high?
Or what if she threatens you? She'll divorce you and say you molested the kids. She can call the cops and say you tried to rape her (and even if the case if thrown out quickly, it can still be devastating). And if you physically resist, that's great - until she get injured (even slightly), then the story will be that you attacked her.
I'm not saying that this is very common, or that men need to get all paranoid. But just because someone's half your size doesn't mean they can't get leverage over you.
In general, I think there's often biased language where there's disagreement. Not that this isn't a problem, but I don't think it's a problem unique to this situation.
Maybe I'm overemphasizing language, but you do have to push people to even realize that there's even a debate to be had. His girlfriend lied to get pregnant and wants to keep it, who cares, he had better upend his life - end of story. Even when there's an awareness of how much that sucks there no 'maybe it doesn't have to be that way' spark of inspiration.