Setting up extreme scenarios to make a point is, of course, one of the oldest rhetorical devices known to our peculiar species. But Robertson's deranged scenario does not fall into that category, because his premise -- that atheists literally believe that since there is no "right" or "wrong," any and all manner of behavior is acceptable -- is categorically untrue. His "premise" is not extreme so much as intellectually dishonest from the outset.
It's an important distinction to observe, because people such as Phil Robertson have real boundary issues with politics and religion. For Robertson, politics must be informed by religious precepts, and therefore religion is inherently political. There is no compromising this dynamic for him and his audience. In this, there is a startling resemblance to how your Islamic Republics and variegated terrorist movements operate.
Is Phil Robertson going to start beheading unbelievers? Of course not. For one, it might damage his ratings. But don't doubt for a second that he views them as second-class citizens -- and more perniciously, as the usual traitorous fifth column damaging 'murka's greatness from within.
The notion that there might be an opportunity there for fruitful dialogue, a rigorous exchange of ideas, is fanciful at best. Robertson is not attempting to evoke Kant or whoever, he's affirming for his audience the basic idea that atheists are amoral assholes who are gonna get what's coming to them, whether by divine retribution or simple home-invasion karma.
The target audience will not challenge him for the same reason they don't challenge serial prevaricator Ted Cruz, who seems to be determined to live down to the "Palin with a penis" standard he initially set. That audience doesn't give two shits that the IRS actually has only 14,000 agents and not 110,000 (as Cruz asserted), nor that it would be stupid to use them to guard the border. It sounds good to them, it affirms their imaginary grievances and ludicrous grudges.
Nor does it matter to them that Scott Walker sounds borderline retarded when he tries to talk about foreign policy. It's one thing to assert (however false) that Iran and Israel seem to have traded places in our foreign policy pecking order, quite another to say that it's like the movie Trading Places. (Personally, my favorite scene in that movie was where Ralph Bellamy tries to explain to Iran -- or maybe Israel; again it's unclear who Walker thinks is whom -- what bacon is used for. And ironic, amirite? Because, you see, neither Jews nor Muslims are supposed to eat bacon. Thanks for coming, remember to tip your waitress.)
Of course we're all used to this nonsense, inured to the reductio ad absurdum nature of political rhetoric. But it's now more like reductio ad nihilo, their bullshit doesn't even make sense anymore, because it doesn't have to. They know their audience, and the most important characteristic of that audience is that they don't care about facts.
Actually, even that's not quite accurate -- it's more than not caring about facts, but more like a hostility to facts. Debunking Cruz' lies, or pointing out that Walker is a fucking maroon who doesn't know what he's talking about, isn't just a useless endeavor, it's liable to provoke them.
It's a shame that that's what it's all come down to -- a political system owned and operated by indifferent psychopaths, who use their pelf to rile up the emotionally damaged and the certifiably insane over phantom issues. When Jay Gould said he'd hire half the working class to kill the other half, he wasn't kidding.