Bear with me for a while, but let me explain why I believe they put the MSM checkbox on the forms for donation:
First the facts:
a) It's pretty much a given that MSM have one of the highest rates of HIV infection. Yes, it might be a large generalization of our population, but it's a statistically accurate one and something that we have to deal with.
b) The screening tests blood centers use (as well as the conventional HIV tests) are forms of what are called serological tests. Serological tests look for the bodies natural response to the HIV virus. They do not directly test for the virus itself. This is the reason why they say you must be tested 1 month, 3 months, 6 months, and 1 year after potential exposure to HIV, because it takes time for your body to mount an immune response against the virus, and in some people it can take up to 1 year.
c) There are two types of serologic tests that all blood donation centers will run to screen for HIV. The first is a screening test that has high sensitivity, but low specificity, which means that it's ~99% likely to pick up any HIV (type B at least) antibodies in an infected persons blood, but it's also noisy and likely to pick up other things that aren't HIV. The second test is a more specific test that they run on the blood that flags as positive using the first test. Combined, these tests have a 99% specificity rate, which means that it's likely they will always find HIV in the blood of a donor who is HIV positive.
Now, knowing the above there are two very good reasons as to why they prefer MSM do not donate blood:
1) In order to save money on screening (it's rather expensive to screen everyone individually), all blood centers pool samples of blood from about 40 donors and then use the first test on this pool. If no one tests positive from the first, very sensitive test, then they consider everyone in that batch HIV-. If, however, one person flags positive, they go through every single donor's blood and run the second, more specific test. Now you can imagine that it's pretty expensive to screen 40 people, which is one reason why they are taking precautions against having HIV infected blood pooled with the normal blood in the first place.
2) More importantly, if you are newly infected (ie HIV+) and have not yet mounted an immune response (remember this could be up to 1 year after exposure! although its more likely to be within 1 month), then any blood you donate will *not* register as positive in the screening process, even though you are infected, and the blood will go unflagged and be transfused into a helpless recipient. Ie you will unwittingly transmit the virus to the donor recipient, because you won't turn positive on the tests until 1 month-1 year later even though the virus is already replicating in your body. This was the reason why 4 recipients of organ donations became HIV positive recently(the first case since the screening process was adopted), because the donor was newly infected with HIV and failed to register on the screening tests as HIV+. Those 4 recipients are now HIV+ (and hep C + too to boot)
So I understand that its frustrating that we can't help out and donate blood, but I wouldn't want to transmit HIV to someone, and I don't think anyone here would either. So in reference to your friend who gets a "free" HIV test through this process, please ask them stop and reconsider what they're doing. It's not so much a political thing as it is a safety issue. The diagnostic tests are not 100% accurate and don't pick up new (less than ~ 1 month) infections.