A few weeks ago, Republican presidential hopeful Herman Cain sat down with ABC’s Christiane Amanpour who asked about his fear of Sharia law being “infused” into the U.S. judicial system. The host, seemingly bewildered by the nonsense, asked, “You don’t really mean this, though, do you, Mr. Cain?” He said, “Oh, yes, I do.”

I thought of this when CNN’s Piers Morgan chatted with Cain last night and the conservative candidate insisted that sexual orientation “is a choice.” The host seemed rather amazed — and ended up using the identical question Amanpour raised earlier.

MORGAN: You believe people — seriously, you think people get to a certain age and go, I think I want to be homosexual?

CAIN: Let me turn it around to you. What does science show? You show me evidence other than opinion and you might cause me to reconsider that…. Where is evidence? […]

MORGAN: Wait a minute, let me ask you. You genuinely believe millions of Americans wake up in their late teens normally and go, you know what, I quite fancy being a homosexual? You don’t believe that, do you?

CAIN: You haven’t given me any evidence to convince me otherwise nor has anyone else.

Eventually, Morgan said this is tantamount to a gay person telling Cain his chose to be black. “Piers,” the Republican said, “this doesn’t wash off. I hate to burst your bubble.”

To which Morgan replied, “I don’t think being a homosexual washes off.”

What struck me as interesting wasn’t just Cain’s profound ignorance, but also Morgan’s incredulity. This seems quite common among many in the media — sure, Republican candidates repeat a lot of nonsense, but underneath the rhetoric, even conservatives have to be more sensible than they appear.

But therein lies the point: they’re really not. Cain actually believes this garbage.

As for Cain’s alleged interest in evidence, Zack Ford recently explained, “If Cain has not seen ‘the science,’ he clearly has never bothered to look. Based on decades of research, all major medical professional organizations agree that sexual orientation is not a choice and cannot be changed, from gay to straight or otherwise. The American Psychological Association, the world’s largest association of psychological professionals, describes sexual orientation as ‘a complex interaction of environmental, cognitive and biological factors.’ There is considerable evidence to suggest that biology, ‘including genetic or inborn hormonal factors,’ plays a significant role in a person’s sexuality.”

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.