Well, maybe the idea is that the man does not discover it is there before he really discovers it - and then he will probably have other things on his mind (like getting those hooks out of his sensitive area).

One big problem with the whole anti-rape condom idea, though, is that you would have to say to yourself: "I expect to get raped today, so I better wear this". Furthermore, due to the mechanics of the thing, you might argue that there would still be an actual rape, it would just be - how to put it - shortened somewhat...

But I agree, it's not a bad idea.