I'm also aware of the statistics - roughly split between gays and heterosexuals. I think the problem lies more with the epistemological side of things. As the marrow registry, how do you know whether or not someone is gay? How do you know whether someone is HIV positive? Only one of these questions actually matters for donors, and only one of them is scientifically testable.
I'd agree with people who are okay with profiling if there wasn't a reliable test for HIV, or if there weren't enough resources to test for it, but I haven't found any evidence for either of those potential claims.
To hell with screening, if I was on death's door courtesy of leukemia I'd rather accept a transplant from someone I know is HIV positive. My logic: given the state of anti-retrovirals, being HIV positive sounds downright cushy compared to dying of leukemia.
I'd agree with people who are okay with profiling if there wasn't a reliable test for HIV, or if there weren't enough resources to test for it, but I haven't found any evidence for either of those potential claims.