That's not necessarily what they mean by "open;" it means if they show up on base on Monday and someone asks them how their weekend was they can say "I went to the lake with my boyfriend" and not risk getting kicked out.
Having been around a lot of gay men for a fairly long period during college I'm a bit mystified about the idea that they're constantly accosting or molesting straight men; or making out in public. I've never seen or experienced either.
Then again there are those of us who do these things. Besides, you have those who consciously set themselves apart from "straight" people. It can be a kind of rejection of normal relationships, a culture that excludes those who are "different." It is this culture that is a threat to the cohesion of the unit.
That's because you've probably only been around those who understand they made a choice to live counter to mainstream culture and they respect the culture as it is. But when you come face to face with a homosexual activist or someone who wants only to shock, or get attention, you have a different circumstance all together.
I too was around several gay men during college. They stayed away from the normal venues, created there own little cliques and were for the most part happy. They did not attempt to force others to accept them. They did not tell others they had to like it. They did not try to convince everyone else that their choice was something other than disgusting to 9% of the culture.
The military CANNOT tolerate cliques or counter-cultures. They cannot tolerate even having the CHANCE that somrthing like that might happen. And finally, they cannot spend time on the battlefield worrying about the rights of gays versus straights. WE DO NOT HAVE TIME TO DEAL WITH THESE ISSUES IN A TIME OF WAR.
And in the military, any minute of any day could e the start of a war. It's not possible and it's not right to the 98% of the men who abhore the practice. These are by design callous, hard-hearted, blunt men. I don't think we want our military investigating claims of being called a "Fag" or a "Fruitcake" on the battlefield.
You may want to be nice and think that gays fight just as hard as straight men, and perhaps they do. But the damage of them being there mitigates the benfits.