"Not all gays have HIV"
You are demanding impossible perfection, ALL of them don't have to have HIV for it to be a health risk associated with that group. And in the US, they(male homosexuals) represent about 2% of the population yet are spreading HIV far faster then both heterosexual women and men combined, in fact, it is the fastest way it is transmited!
Cumalative Diagnosis
Male-to-male sexual contact 441,380
Heterosexual contact 159,114
http://www.avert.org/usastatg.htm
And I could use your "All or nothing" illogic to justify just about anything. As long as atleast one member of the group isn't participating in the negative activity etc.. you can't discriminate (in your world that is).
Some of the attitudes/opinions on here are amazing.
Should we have a DADT policy on race, too? I mean, racial problems probably have some affect on serving. Before you blindly respond to this question, think about it. Think about it well.