Except it’s not just the Red Cross. (Or does the Red Cross set the defacto standard?) The place I give is unaffiliated (as as I can tell) and has the same requirements. (I especially like the one asking if I’ve ever been to Central Africa. I guess you’re instantly contaminated the moment you step off the plane…) The reason, of course, is liability in case someone receives some horrible disease due to receiving tainted blood.
No doubt matt_mcl shouldn’t be prevented from giving blood just because he’s gay. Unfortunately, I expect if someone were to contract AIDS from donated blood and the collecting organization’s screening process came into question, people would be quick to sue just because of homophobia.
Granted, that’s just an excuse, and not a very good one. People are scared of these pretty horrible diseases they don’t understand, and scared, ignorant people don’t always think logically.