3) is the only one you gave a reason for so its all im going to address, I'm not going to debate against statements made without any kind of arguement behind them.
Like I mentioned, people in the service already have sex with other service members. And unless you are going to tell me that gay people have less control of their sexual urges than normal people, just because they are gay, you have no arguement. I'll give you an example, I know several couples who work together in the same building at my base. They can manage to not have uncontrolable sex on the job. And crazy as it sounds I know, gay people can have that kind of control too. In fact I would be inclined to believe gays can control their sexual urges better in places where its not welcome, because of the negative image associated with it. Now in the Army there's no "PDAs" public displays of affections, couples aren't even supposed to hold hands in uniform and on the job, gays will be given the same rules as anyone else.
Lastly, do you think that no straight people have engaged in orgies? I'm pretty sure its safe to say some have done it in SF bath houses too. Should we ban straight people from the military because of that kind of "stuff?" Or is there a double standard because they are gay? If thats the case I'd ask why there is a double standard, is it just cause you think its gross?