NOTE: Was responding to this and it got too big.
A friend of mine in the Army explained to me once, why the bulk of servicemen from the top officers to the lowest enlisteds are against the allowing of open homosexuality in the Armed Forces. Primarily, it was unit cohesion, and he gave me an explanation, that I thought made sense.
Unit cohesion depends upon members of a unit trusting each other with their lives - no favoritism, no hesitation. Sex brings all of these things back (and heavily) into the equation. This is the reason why allowing gay men to serve in the Armed Forces is not in any way related to desegregation - there is no equivalence (of military import) between them.
There is a reason why brothers and other close relatives are not allowed to serve in the same unit where they can conceivably fall under the same command line - and where one may possibly command the other directly.
The Armed Forces do their best to avoid such situations not just because they want to avoid "Saving Private Ryan" type situations but also because they want to avoid having situations where one brother has to, for the sake of the mission or the lives of other members of the unit, command his brother (because of a specialty in his training) to do something that would almost certainly mean he gets injured badly, or even his death.
The psychological impact of giving an order and a man of yours dying or being maimed in order to carry it out is not something many outside the military (and rescue services) can contemplate - the guilt, second-guessing, the self-recrimination, can destroy all on its own.
Now imagine if that man was your brother.
Allowing open homosexuality into the Armed Forces presents the same issues. One single gay man in a unit may not be much of a problem - it's entirely possible (if difficult to imagine) that his unit mates would not really care that he prefers men to women as sex partners.
It's when you have two or more gay men in a unit that you may have a problem. Fighting units live in close quarters with each other, and their members are at the peak of fitness and I would assume, attractiveness. It's the same problem that presents itself with putting women in combat units.
How do you stop relationships from forming? L/CPL A and Private B competing for the affections of Private C to the detriment of the rest of the unit that will almost certainly be aware of it? Note that A, B and C could be any combination of genders. Private C could be a woman or a man.
Imagine the battlefield again, CPL A has to order his lover, Private C, the specialist in X, to go do X. If X is not done, the platoon is not going to make it without suffering heavy casualties. But the person doing X, while saving the rest of his/her unit and helping them achieve their objective, is not likely to make it back.
So the Armed Forces are back to square one. Avoiding putting brothers in the same units is fairly easy. Limiting the mixing of men and women in order to prevent the formation of complicating relationships is harder, as the Navy has discovered with the phenomenon of female sailors falling pregnant while at sea. Three guesses who's impregnating them - civilian tag-alongs (i.e. NCIS), aliens or their male fellow sailors?
Now we're asking them to find a way to ensure that gay servicemen are distributed enough to minimize the risks of sexual relationships forming between members of the same unit.
Somehow, I don't think this is likely to end well.
The floor is open for discussion.