Problem is that gays are prone to HIV/AIDS.
Other troops will fear to be exposed to them in situations where hetero’s could be contaminated by homo bodily fluids (training, combat, injury treatment—not just consensual peanut butter packing in the showers).
Homo behavior is high risk behavior, that if it applied to say, guns, would be banned.
Every man in combat is a potential blood donor.
Everybody in combat is considered to be a blood donor.