homosexuals serve in combat units now, and always have.
yes, however, prior to this they weren't allowed to be open, which meant no relationships and no real possibility therein, which translated to the effect on the
unit being as though there were none. that was the elegance of the DADT compromise which it's opponents so blithely ignored.
Women do not and have not served in US combat units.
and thank goodness. because where they go, such issues inevitably arise; and the combat units don't have the time to afford for such things.
Second, the majority of men and women are heterosexual. This means that with a unit of 50 personnel, if 3 were women (say, 1 gay, 2 straight) and 2 were homosexual men and the rest were heterosexual men, the chances of an actual relationship starting between anyone is most likely to happen between one or both of the two straight women and one or more of the 45 straight men. The two straight women have a choice of 45 men (with everyone's sexuality known). The one gay woman doesn't have a choice of anyone in the unit being compatible with her sexuality. The two gay men only have a choice of each other. And the 45 straight men have a choice of 2 women.
the problem isn't when there are two gay men, it's when there are three; and two of them are in a relationship... until one of them decides to cheat on his partner with a third.
and so on and so forth. the problems that come with the introduction of sexuality into a unit are legion, from jealousy, to cliqueishness, to backbiting, to distraction.
Also, you need to actually prove that a) sexual tension causes a significant reduction in cohesion
really? in a world in which commanding generals have to say "oh by the way, even though we've ordered ya'll not to screw each other in country, there are too many females getting pregnant and so if you do we're gonna charge you" i have to demonstrate a reduction in cohesion?
take a bunch of mixed-gender 18-21 year olds. put them close together in a highly stressful situation. they
will think with their private parts.
b) the sexual tension between sexualities is comparable to that between opposite sexes in a mostly heterosexual environment with mixed genders
if we are to believe some of the statistics floating around there about the average number of partners for a homosexual male the problem is arguably worse.
c) there are not other rules/policies in place that deal with any tension that some may face that could significantly affect unit cohesion.
this is sort of like arguing that you can regulate "no being human".