When a person says something you disagree with, start with “does that make sense to me?” as your first reaction. If it doesn’t make sense, move your thinking to “why are they saying this? And does this tell me something new about this issue or their experience with it?”
A default reaction of “they’re just dumb” doesn’t open up your mind to other possibilities. It diminishes the humanity of the other person. It leaves no room for forward movement.