I have a sort of recipe for openly discussing disagreements with someone:

1. Demonstrate that you understand their point, and concede ground where necessary (what you think is attractive about what they are saying, what it explains well, etc)

2. Explain (not tell) why it is that in spite of that, you don't hold the position they do (maybe it leads to some other conclusion, maybe there's another core principle at work)

3. Ask, with genuine curiosity, what they think about the problem you raised, how to they resolve it in their mind?

I don't think that'll necessarily make you more likely to change their mind, but you'll certainly be more likely to learn something.

And if they aren't actually interested in discussing, and are just engaging in some kind of show boating etc, it will become immediately clear because you are only leaving open the possibility of curious, open dialogue.