Fine, now, let's go back to the very beginning of this year. Remember the big news story? In Tucson, Arizona, Congresswoman Gabrielle Giffords and others were shot. Six people died. Congresswoman Giffords was gravely injured.

Jared Loughner was arrested at the scene of the crime and it was immediately apparent that Loughner is an extremely disturbed man. Still, countless liberals pointed fingers at increasingly extreme rhetoric on the political right. Maybe it was a direct cause. Or maybe it only contributed to an environment that could set off a nut. Either way, it was dangerous and wrong, they said.

"Gradually, over time, political rhetoric used by politicians and the media has become more inflammatory," wrote former U.S. Senator Gary Hart in the Huffington Post. "The degree to which violent words and phrases are considered commonplace is striking.

Candidates are 'targeted.' An opponent is 'in the crosshairs.' Liberals have to be 'eliminated.' Opponents are 'enemies.' This kind of language emanates from those who claim to defend American democracy against those who would destroy it, who are evil, and who want to 'take away our freedoms.' " This sort of "irresponsible and dangerous rhetoric" must be not tolerated, Hart concluded.

There were countless commentaries like that. "A widespread squall of fear, anger, and intolerance" has "infected the political mainstream with violent imagery," the New York Times editorialized. "Even if hate is what many want to hear, that doesn't excuse those who pander to that desire," wrote Times columnist Paul Krugman. "They should be shunned by all decent people."

That was seven months ago. This Tuesday, New York Times columnist Joe Nocera called Tea Party Republicans "terrorists" who "have waged jihad on the American people. Their intransigent demands for deep spending cuts, coupled with their almost gleeful willingness to destroy one of America's most invaluable assets, its full faith and credit, were incredibly irresponsible. But they didn't care. Their goal, they believed, was worth blowing up the country for, if that's what it took."

Nocera returned to the theme in closing. "For now, the Tea Party Republicans can put aside their suicide vests. But rest assured: They'll have them on again soon enough."

Now, let's not get into what is and isn't legitimate rhetoric in the hurly-burly of political debate. The point here is simply the contrast: At the beginning of the year, liberals passionately condemned the violent rhetoric of conservatives; seven months later, a liberal columnist, in a liberal newspaper, launched a rhetorical blitzkrieg.

Conservatives went bananas, naturally. But liberals? There were hundreds of comments about Nocera's column in the Times' website. Most are long, informed, and articulate. Most agree with Nocera that the behaviour of Tea Party Republicans has been astonishingly foolish. (For the record, so do I.) But very, very few condemn Nocera's language, and most of those appear to have been written by conservatives.

So what's the conclusion? If I were ideologically straitjacketed, as far too many columnists are, my ideological commitment would determine the answer to that.

If I were a conservative, I would call liberals stinkin' hypocrites and my ideologically straitjacketed conservative readers - the only sort I'd have - would all cheer and feel superior and have a good time.

But if I were a liberal, I'd use all the ingenuity at my disposal to come up with some explanation for why Nocera's violent rhetoric is completely different from conservatives' violent rhetoric and it's completely ridiculous to suggest there's any equivalence whatsoever. Or, like the Times readers, I just wouldn't notice and there would be nothing to explain.

But I am neither a conservative nor a liberal, so I'll draw a different conclusion.

Extreme commitment poisons reason.

Identify yourself with a tribe, work passionately for the tribe, make the tribe's advance your highest goal, and the tribe shapes what you see and think and believe. You still talk of evidence and reason.

You insist your beliefs are determined by careful consideration of all the facts and competing arguments. But this is nonsense. In reality, the facts and arguments you cite are determined by your beliefs, and your beliefs are determined by the tribe.

All this is obvious in the other tribe, the bad tribe, the dishonest and deluded tribe. But your tribe is entirely free of this irrationalism. Why, it is precisely because your tribe is reasonable that you adore it.

Am I right? For the committed conservatives among you, were you delighted to read about liberal hypocrisy? Yes, you were.

And you committed liberals: Were you vaguely annoyed? Did you find yourself struggling to come up with some reason why violent rhetoric directed at the other side is completely different than the violent rhetoric of conservatives you condemned seven months ago? Of course you did.

Bear in mind that I could have written the same column using a conservative blind-spot as the illustration. In fact, I did, some time ago. I got angry e-mail from conservative, praise from liberals, which nicely underscored the point.

This isn't a liberal or conservative thing. It's a human thing.

And personally, the effect this has on public discourse worries me a lot more than violent rhetoric.