I donate blood every few months, get lots of free shirts out of that are comfy and awesome to show off "Blond Donors Save Lives" and such. But I don't agree with the idea that if you don't you kill 3 people. That's extreme. Though I'd suppose it'd be almost accurate if there became a serious blood supply shortage and no one was donating, then that is almost as bad. I just see if there's a few dozen people per event then everything's a-okay with me then.
EDIT: As for the people who are upset with the no gays, they don't care if you're gay, just if you've done gay oral / anal sex, because gays have no reason to use protection other than for possible spread of HIV, thus much easier to spread among your population. Not saying it's a smart rule, anyone can get it, just a lot more among the gay population, and I can semi-see their reasoning... as flawed as it may be, however.