With friends like you who needs friends?

I've been mulling lately over what we expect of our friends. When your friend is attacked by others but in the wrong, do you close ranks and defend him, even if that means disingenuously arguing in favor of his mistaken position, or try to support him without compromising your own ideas of what's right? What do you expect your friends to do for you? Would you rather have your friends admit to you when they agree with third parties that you are in the wrong or keep their mouths shut? (Assume that this is done in the absence of said third parties and you do not attack your friend's position publicly.)