Etiquette refers to polite behavior. I think you’re talking about morality.
Frankly, I don’t know enough about your friendship. I’m not the political version of Dear Coke Talk — I’m not going to assume stuff. Is there an equal exchange of views between the two of you? Is he a completely unreconstructed Neocon? How tight is his cocoon? Have the events of the past 10 years had any impact on his politics? And if so, why is he still a Neocon? Does he budge in the face of a convincing argument? Or does his paycheck require that he adhere to a certain party line?
I guess what I’m asking is: Is he a hack? Is he working for one of the big ones or the smaller ones? All think tanks are not equal. There are 3 strands to American conservatism: the bible-thumpers, the money-grubbers and the war-mongers. If he’s at Christian Coalition or something, you might make some headway on social justice or the environment. And the libertarians over at Cato are fucking nuts, but at least you can smoke a joint with them after-hours. But if he’s at Heritage or (shudder) AEI, if he’s a true dyed-in-the-wool Neocon, then he’s in the heart of the beast. He’s in the intellectual nerve center of the 2nd Bush Presidency. And we’re not just talking about massive deregulation or a gutting of the social safety net. We’re talking about preemptive war and torture. And they just excommunicated the very last intellectually honest thinker they had.
I, myself, wouldn’t cut ties just yet. Shunning is for the Amish. But keep your North Star. You have a friend who consorts with, and advances the interests of, war criminals.