Before you argue, try explaining their side so well they’d nod along. Then see if you still disagree.

Most arguments happen between two summaries, and both summaries are unflattering. If you can state the other position in a way its holder would accept, you have finally found the actual disagreement, which is often narrower and more interesting than the one you were having. Sometimes it also dissolves, because the version you were fighting was one nobody held.

Before the next debate, write their case in three sentences and imagine reading it to them. If they would object to any line, it is not their case yet. Keep going until it would pass, and only then work out what you think.