You could read this, which makes it sound like there was an actual rational discussion on This Week about repealing DADT (and there was, sort of -- but only with some of the participants), or you can take my word for it that the the two far-right nutjobs who came on to plead that allowing people to be openly gay in the military would undermine the nation's mission (I guess because they'd all be off organizing drag parties or Gay Bingo Nite) are just plain barking insane, and swimming upstream against reality.
But the entire argument against repealing DADT was distilled in one statement by director of National Security and Joint Warfare at the Marine Corps War College Tammy Schultz and reinforced by R. Clarke Cooper, an Iraq War Vet and member of the Log Cabin Republicans, who are spearheading the campaign for repeal:
SCHULTZ: Nothing will be good enough for the opponents who do not want to repeal "don't ask/don't tell." It's not about the evidence; it's about the ideology. They're saying, oh, you can't compare the U.S. military to other militaries. We're bigger, we're in war, et cetera, et cetera. But then they simultaneously want to say we have the most professional forces in the world, which we do.
And that's true of almost all of conservative obstructionism. Nothing is good enough to knock them out of their world view: no facts, no studies, no other opinions. And no matter what you say, they'll constantly stay with their unsubstantiated talking points.
But at least Christiane Amanpour challenged them. A little.