There isn't really any sound reason to keep gays out of the millitary. The one that is used is that it will be a moralle problem but give me a break, like integrating gays would be so much more difficult than integrating blacks, durring the korean war, while the KKK was still lynching them in the south.
Obviously no one would want to hand the queer eye guys a gun and say "go defend our boarders" but if the drill seargents could handle the naive boys of WW2 or the 'hell no we won't go' crowd from the 70s or the loser goth macdonnald employees of today, they can turn anyone into a soldier.
As research into the history of homosexuality has come to light we've found much homosexuality in the ancient armies such as the Theban Sacred Band who where the Army Rangers of their city-state and was composed of 150 pairs of male lovers.
So there is no historical evidence to suggest that homosexuals are any less capable of warfighting, only cultural perceptionary problems.