Good question. I’m sure it is necessary to test blood for all types of things i.e. hep c, hiv etc. At the beginning of the AIDS thing, I remember that they would not take blood from homosexuals but of course there was an ‘outcry’ so that got nixed.
When you give blood one of the questions on the screening questionnaire that they ask is if you have had sex with a man recently. If you answer in the affirmative you are declined.