cutting someone with card throwing? Although I see the potential of doing that, the Mythbusters proved that it's almost impossible for a human to draw blood by throwing a card at someone. They even had Ricky and Chris to test the myth. Neither one of them cut anyone, let alone lodge a card into ballistics gel (equivalent to human skin). It took a machine that shot cards to get any damaging results.
Not my opinion, just what I've seen.
Back on topic, I practice card throwing a lot and I've gotten pretty good at it. Never cut anyone.. never tried lol