Many hold strong beliefs and opinions, however not many know the roots of their belief. If a person agrees to explore it, both of you will learn something new and fascinating. The problem is finding someone who wants to think and ask the questions. This goes for both. Many want to “convince” someone, but how much do you truly know about the thing you’re trying to prove?
This also comes back to the “why?” game so many kids play. Parents get annoyed by it, but are they really annoyed at the game or their lack of knowledge depth? Play the game, find out how deep you lake of knowledge goes
I think the key is to remember you are trying to discuss opinions/convictions not facts.
When B says something like “C is a nazi”, A correctly asks why B believes C is a nazi, not why C is a literal nazi. So when you go down one level, A’s next question should be something like “why do you think these are nazi tactics?” and “why are nazi tactics bad?” It really requires both sides to be intellectually honest and curious about someone’s actual beliefs, otherwise the technique doesn’t work. I also think limiting yourself to just “why” isn’t always helpful. Sometimes you need to ask for clarification or the entire conversation becomes a farce.
Remember the goal is to learn something about the other persons views, not to set each other up with rhetorical questions.