You wouldn't know if any of your friends is a rapist. It's not like they would tell you.

Edit: Even in the case of these guys, my other comment still applies.

Most of them genuinely believe it, too. Everyone knows rape is evil, and everyone thinks that they're a good person, and since good people don't do evil things, they can't be rapists. They'll do all kinds of mental gymnastics to avoid critically examining whether any of the sex they've had was actually rape. She was asking for it, he couldn't help himself, she didn't say no, she was into it at first, she was leading him on, she just wants attention. These guys will come up with any excuse that keeps them the "good guys."

They knew that their friends were having sex with a woman, and failed to critically examine whether that sex was in fact rape because the idea that their friends might be rapists never crossed their mind. We all need to be aware that we are capable of doing evil things.