When it comes to homosexuals, the one homosexual that comes clean in a Marine Infantry unit will be ostricized and humiliated quite often. A Fire Team consists of 4 people. If one is gay, then this fire team is void of the very important cohesion it needs to perform. This carries on into larger units.
Now, correct me if I'm wrong, but if men have a superior attitude towards women in the work place (because they lack the manly penis of the boys club), then certainly they have an even bigger superiority complex towards the man who has a penis and desires to use it with other peni. There is a certain amount of common sense that one should apply to assuming the probabilities rather than pretending that walking around in the dark is the only way to go.
The biggest problem people have with this is that they think about flambouyant gays when they think about "serving openly." But flambouyancy is a joke for Hollywood and the Air Force, not the ground forces. Most gays (virtually all in the Corps) will choose to remain private in their sexual abnormalities just for the sake of making a life in the military easier.