Open homosexuality does not change just DADT. Once that happens they will have to change DOMA, allow marriage and let them move into housing. And THAT will cause problems.
There is no good reason to do this and every reason not to. Service in the US military is not a right. Every country that has allowed it is a shell of their former military selves if they were ever any good at all. Open homosexuality is not the cause, it's a symptom. But it is real.
It is much like the females. We kid ourselves. We say "They are fully integrated, they're just as good, it's ok." In some cases it is close to the truth. There are some very good female soldiers. No matter how good they are, they aren't the same. And we don't do different well.
Black soldiers are no more "fully integrated" now than they were 30 years ago. Anyone that believes there isn't racism in the Army is a fool. And not just a bit. And not just one way.
The Army is falling apart and this will do nothing but hasten the problem.