In summary Gay men DO have a higher probability of being infected not the same chance.
It's not just probability. 3/4 of new HIV diagnoses are male, and about 2/3 of those cases are through male-male sexual contact (about a tenth are through heterosexual contact - the remainder is mostly through intravenous drug use, another group which cannot donate blood along with people who have lived in several countries of Africa, and people who lived in Europe during the mad cow disease outbreaks).
Ultimately, it's the transfusion recipient that's burdened with 100% of the risk, and it's better to protect the people who stand to get hurt, than the feelings of a minority group.