In How to Win Friends and Influence People, Dale Carnegie recommends saying, "If I were you, I'd do the same thing," on suitable occasions. He reassures the scrupulous that it's not a lie: if you were him, by definition you'd do whatever it is that he does.
I don't usually care to shave things as finely as that. (Neither, on the whole, did Carnegie; his book has lots of good advice that can be used without malicious intent.) But I do find myself saying things like, "If I believed what you believe, I'd do what you do."
(And not just to Rob in the comments here.)
There are many cases where the conclusion of an argument is true only if the premises are true. (For example: He committed this crime, so he should be punished for it.) If I don't accept your premise, I'm not going to accept your argument, and I'm unlikely to accept your conclusion (though I may accept a different argument with the same conclusion).
It sounds obvious enough when stated, but I think it's common for someone to find a certain premise so blindingly obvious he never bothers to prove it to people who don't accept it. He simply restates or polishes his argument based on that premise, and cannot understand why others refuse to accept his conclusion.
Evaluating arguments for validity ("Does the conclusion follow logically from the premises?") is the (relatively) easy part. Evaluating them for soundness ("But are the premises true?") is the hard part, and often enough a matter of subjective judgment ("But is he a louse, or just a bum?").
Disagreement is often based, not on the conclusions, but on the premises. Maybe that's one reason disagreement is so hard to reach.