Have you ever had to deal with someone over a dispute and after "taking all day" felt you got nowhere? That's a common problem.

What you have to do is focus on the core issue. Just interrupt and say, "Look, we both want to resolve this dispute. The only real issue here is X. Until we resolve that, I'm not going to talk about anything else. It would be pointless to do so."

When you feel something is dragging on and getting nowhere, that is happening because nobody has really defined the terms of the debate. So, define them. And then hold the other party to those terms.

Here's another scenario. Bob has crafted an opinion based on misinformation. You know this, and you disagree with Bob. You've told him you will have to agree to disagree, and you don't want to "go there" anymore. Yet every time you talk to Bob, he wants to argue his opinion at you. Bob is simply wasting your time with his stupidity. This really isn't about Bob's wanting to understand the truth and your needing to be persuasive. It's about Bob's wanting to save face because he knows he's wrong. You have several options:

1. Just agree with Bob, so he shuts up about it. This isn't honest.
2. Find an article, from an unimpeachable source, that authoritatively settles the argument. This may cause Bob to counter with poor sources of information.
3. Tell Bob you are finding his pursuit of this annoying to you and demeaning to him, and you want him to stop. This attacks the core problem, head-on.