This is a big mistake.
And the mistake is that we should even care.
When an American citizen raises their hand, takes the oath of enlistment or commissioning, committing themselves to defending the constitution and expresses a selfless wiliness to place themselves in harms way for something more important than self, then their sexual orientation doesn't mean jack.
Our troops are the best trained, best equipped and most professional in the world. They will be able to handle it. The dire predictions about troop moral and retention problems will turn out to be a load of crap.