All blood is tested, but the tests can return false negatives fairly often.
You are also prohibited from giving blood if you've had sex with a prostitute, lived in some countries, or had a variety of medical treatments.
Even by testing every donation and prohibiting a large number of people from donating, people still get incurable diseases from transfusions. This is not political by any stretch of the word. Blood centers literally never turn down blood, they take all they can get. The idea that not accepting blood from males that have had sex with other males is some sort of moral or political decision is reprehensible.
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"What if you just eat vegetarians?"-neonreaper
"^ You are what you eat. ^_~"-Koiji