gay blood donors exist

Gay blood ban
It's my belief that the ban on gay blood donations should be overturned.
The ban is patently discriminatory, based on stereotypes, but justified under the mantle of medical science. It's just one example of how rank prejudice is remade as scientific, sanitized, made to appear ethical.
Technically, the ban is on a man who has "had sex with another man, even once, since 1978". There is no ban on women who have had sex with a man, although there are specific categories of male sexual partners that trigger excluding a potential donor from giving, if she has had sex with them in the last 12 months.

Does the ban "work"?
Does the ban in fact keep gay men from giving blood? The simple answer: no.
The more complicated answer: in the General Social Survey, respondents were asked (in 2002 and 2004) whether they had donated blood in the past year, and also several questions about the sex of their sexual partners. Here are the results, using three different definitions of sexual partners...

Among 36 men who reported at least one male sexual partner in the last year, 6 (17%) said they gave blood in the last year. This is somewhat lower than the 22% of 826 men with exclusively female partner(s) who said they gave blood.

Among 43 men who reported at least one male sexual partner in the last five years, 6 (14%) said they gave blood in the last year, while 21% of 884 men who had sex only with female partner(s) said they gave blood.

Among 58 men who reported sex with at least one male sexual partner since their 18th birthday, 4 (7%) reported giving blood in the last year, while 21% of the 942 men who reported no male sexual partners since turning 18 reported giving blood.

There are good reasons for being a bit skeptical about these data, but more on that later...

Adverse consequences
If the ban on gay blood donors doesn't "work", then is it worth maintaining? What are the consequences of maintaining a patently discriminatory policy?

1) An unjust ban on gay blood donors encourages lying. Anyone (straight or gay) who sees the exclusion of gay men as discriminatory will begin to question the validity of the other screening questions, perhaps taking liberties with answering screening questions that have a valid basis for protecting the blood supply.

2) It justifies discrimination in other areas. The fact that most people believe the screening questions on the blood donation form have some scientific or medical basis makes it appear as though this form of discrimination is beyond questioning. Justification of discrimination in one setting encourages people to justify for discrimination in other areas (even on a different basis).

3) The ban makes it unclear how a gay man should approach donating blood. By having an outlandishly discriminatory donor exclusion policy, blood banks are in effect encouraging each gay blood donor to make up, in his own opinion, when it is safe enough for him to give blood. Whereas a policy in line with the other donor exclusion policies would set a more realistic set of limits that gay blood donors would be more likely to honor.
A consequence of this is that the ban on gay blood donors may in fact make the blood supply less safe.

4) The ban reduces the potential pool of donors, in more ways than is immediately apparent.
4a) It is well documented that gay men are more likely to give altruistically in a variety of ways, thus the ban cuts out a segment of the population that would otherwise be eager to give. Although gay men represent a small proportion of all potential donors, and even though many gay men would be excluded for medically justified reasons (such as having unprotected anal sex in the last six months), the exclusion of a motivated group of potential donors may not be a great idea.
4b) The blatantly discriminatory nature of the ban on gay blood donors has already started to lead to a wider backlash. Some straight men, and women of all sexual orientations, get a bitter taste in their mouth from the obvious discrimination of banning men who've had sex with even one man, even once, since 1978. This bitter taste shrinks the pool of potential donors, probably in much larger numbers than the gay men excluded from giving currently.
4c) College campuses, settings where many people initiate a lifetime habit of giving blood, are also settings where action is likely to be taken against discriminatory policies, and in fact blood drives have been canceled on several college campuses already, with the promise for such action to expand in the future. Can the blood supply afford to lose all these potential future donors?

who are the gay blood donors?
I don't know. I'd love to talk to a few to get a better sense of what motivates a gay man to give blood. How does giving blood relate to a man's sense of well-being? How does being refused the opportunity to do so without lying relate to a man's health? Are gay blood donors much more scrupulous about the other screening questions to compensate for lying on one question? Or are they more likely to overlook the other questions?

data limitations
the number of men who report male sexual partners is already pretty small in the GSS (36-58, depending on which question), and the number of these men who report giving blood is even smaller, 4-6. So, it is possible (if unlikely) that these are all data errors. That is, it is at least theoretically possible that 6 respondents weren't paying close attention when asked either about giving blood, their sexual history, or both questions, and gave answers at variance with their actual experience. Or, the telephone interviewer may have slipped when entering the number corresponding to the person's answer.
In addition, there are good reasons to think that the proportion of people saying that they gave blood is considerably higher than the number who actually did give blood. For one thing, a small handful said that they gave blood monthly, even weekly. Blood centers generally ask donors to wait at least two months between donations, so these answers are highly suspect. The other thing is that over 20% of the GSS respondents reported donating blood, but probably no more than 10% of the population actually does donate blood.
However, my point was merely to document that gay blood donors exist, not to give a precise estimate of how many gay men are blood donors. Better data would be needed to make that estimate.