I have found it helpful to move conversations from abstract ideas to something that encompasses a shared humanity. Abstract is impersonal and so it's easy to have us and them. Humanity is messy and there's lots of grey areas and unknowns. When it comes to debates about issues, I have found it helpful to get people to name what they are afraid of losing. I think as a society we are terrible at assisting people to mourn what was. People fear loss. And they will fight for whatever it is that they feel they are losing. Especially if they somehow feel it is attached to their identity. Forget if an argument is rational, you pointed out correctly that trying to change someone's mind if a waste of time. Instead, get them talking about a personal story and then relate to that story and connect with them. They will no longer see you as a threat to whatever it is that they feel they are losing.