Non-insane conservative Dan Drezner points out that even if repeal of DADT has some modest and temporary negative effects on things like unit cohesion and combat readiness, the status quo is having way bigger negative effects:
I therefore really and truly don't give a s**t why John McCain's position has shifted. I just want to know why the ranking minority member of the Senate Armed Services committee is throwing national security, civilian control of the military, and the hierarchical chain of command under the f***ing bus. John McCain is weakening the institution he claims to love the most. I don't care why he's doing it — I just care that he's doing it.
This is really not going to be a shining moment in the history of the conservative movement. You'd think they might have learned their lesson on basic civil rights questions back in the 60s, but no. They're hellbent on replaying their worst moments.