I've isolated three different ways I tend to say it, so I thought it might be nice to translate for you.
I'm not arguing with you. I'm just saying.Usually, this comes up when you've made a particular point and I agree with it. I'll typically start my rebuttal with something like, "Well, I agree, but I can see their point," and proceed to play Devil's Advocate. This is usually quite interesting for both parties, but it does have the potential to get heated -- which it shouldn't, because a) you don't have to convince me, since we already agree, and b) I don't want to convince you, since we already agree. Therefore: I'm not arguing with you.
You know what? I'm not arguing with you.We disagree about something trivial. I'm not going to convince you; you're convinced you're right. You're not going to convince me; I'm convinced I'm right. But in real life, it makes absolutely no difference who is right, so why, exactly, are we arguing? I'm not giving in, but if you choose to believe I am, that's fine. I'd rather stop this stupid fight than win it.
I'm not arguing with you. It was just an idea.I suggested something. You responded, "Well, why would I want to do X?" I don't actually care that it was meant as a rhetorical question; I'll tell you why you might want to do X. But that doesn't mean you have to; I'm just answering your question, not trying to convince or strongarm you. Now that you've listened to my side of it, go ahead and say no. It's fine. It was just an idea, not an argument.
Is there a phrase you find yourself using? What, exactly do you mean by it?