Some stances are just so obviously wrong that it’s hard to understand how anyone can even come to that conclusion.
The natural reaction is to just dismiss the other argument: What’s going on with you? (Which easily leads into pointless fights that lead nowhere.)
A much better approach is to turn that feeling into a genuine question. Really, what’s going on here? What brings them to that conclusion? As, from my perspective, this argument is so obviously wrong that there must be something going on here. Really, what?
Often, it turns out that there, in fact, is a reason to come to a different conclusion. Or, at least, a cause. Addressing that cause can lead to way more meaningful discussions. And to way more meaningful reactions to deal with a situation.
(A simple example: As a business owner, we are sometimes baffled about why a customer didn’t choose us, right? What’s wrong with them that they really considered our competition the better offer. Asking a genuine question about what the hell is really going on there gets us much more meaningful answers – and, consequently, much more meaningful reactions to adapt our offer.)