QM - no other countries in the West have a problem - not so. Most European countries, unlike the UK , have indefinite referral. The UK has 1 year deferral. Only three, Poland Spain and Italy have no ban.
http://en.wikipedia.org/wiki/Gay_male_blood_donor_controversy
As LazyGun explained earlier deferral exists because of the higher incidence of HIV in that population and because of the window period, where one is infected, but it doesn't show up in the blood test thereby giving a false negative - it's all to do with medical risk, and nothing to do with morality or homophobia.
Doubtless when the incidence of HIV declines the restrictions will be lifted.