I've always hated it when I'm reading one of these and the "aggressor's" whole rational for doing this to someone even when they're struggling and pleading is "you say no, but your body says you like it" or "you wouldn't be so aroused if you didn't like it." Christ, that's such stupid logic!
It's like most hentai/ecchi mangaka doen't get the fact that you can literally force someone into a state of arousal/force them to climax. The only time I can think of where someone points out the difference between desire and simple reaction to stimulation is in Mikuni Hajime's "Gokujou Drops" (http://dynasty-scans.com/series/gokujou_drops). I can't remember which chapter it, but it's one of the later ones.
Also... Maybe it's a Japanese thing, but I never understood the whole "arousal = shame" logic that so many of the females in manga seem to have. They're always saying something like "No, don't look!" or "I'm so sorry, you must think I'm some kind of pervert?". But that's just my take on it, as a westerner and a guy...
