Gay men are not allowed to give blood. This is an outdated ban that has no scientific data to support it.
The ban came about during the AIDs scare in the 70's. While many other countries have lifted the ban, the United States stills holds to the policy of lifetime deferment.
Banning gay men from giving blood is cutting off a sector of people with healthy blood to give. Proper testing (which is done anyway) prevents the transmission of contaminated blood.
Allow gay men to give blood allows them to take part in an American right and duty.
For more information, you can also visit http://www.banned4life.org/