Why don't gay men see that it is not discrimination, but a matter of public health?

Ok, let's assume there's a new discovery that says Republicans are more at risk for cancer because of a blood trait that is communicable. Is it fair to prohibit them from giving blood out of fear? There is a test (maybe about robbing babies?) that determines whether or not one is in fact, a Republican. But new converts might still have reservations about beating the infant to death. So, is it safe to discriminate against these people, even when their blood would help others of their own kind?