Well, actually, I think the point that these idiots are trying to make is that there IS no legal argument for consent at all. ALL consent is revoke-able. The example you gave about the coercion, legally (and morally and ethically and logically), is NOT consent.
I mean, with this sort of person, imagine someone going up to you, who you find extremely attractive, and they ask if you want to have sex, then you say yes, you have sex, and then they say "I regret this!". To the people Brujon's linking, YOU RAPED THAT PERSON. They came on to YOU, and YOU did the rape.
What you are saying about consent is right. It's possible to say "yes" and have it not be consent. Anyone who is impaired enough is not capable of giving consent, even if, at the time, they feel like giving consent. This is otherwise known as date rape and statutory rape. And whatever it's called with the mentally handicapped/coerced.
EDIT: btw, my recommendation Brujon, is to just ignore them. These types of "feminists" (note the quotes) are not common. Thankfully. They are very vocal, but not numerous. And much like the sexism from the other side of the spectrum, eventually they will be removed from the pool. Society will eventually even itself out. The BEST thing you can do is prove them wrong about men by acting like a human being. Don't go out of your way to act all holy and saintly, just act like a normal person. Same thing with the other side. Of course, go to the police if things get out of control (like, threats and whatnot). But don't debate them. That only makes them stronger.