I strive to treat people I disagree with as intelligent persons of goodwill. I don't always succeed. It helps that many, even the majority, of my friends and family disagree with me politically.
A reader sent me Evil Greedy Stupid Sheep: 4 Modern Ways to Win An Argument. The only quibble I have is the word "modern". I am pretty sure that if we had better historical sources we would find people accusing Ramses or Sargon of being evil and in the pay of grain merchants.
I would add a fifth category to this I would call "out-group". I don't have to listen to you because you are from group X. There is a famous quote from WWII from a man I believe was in the British Foreign Office, who, when asked about stories of Nazi atrocities, said that they needn't take seriously a bunch of "wailing Jews."
As I grew up, I thought we might actually be getting beyond this. You know - the sixties and tolerance and racial understanding and all that. But it turns out that tolerance does not mean the end of out-groups, it simply means that the out groups are changing. "Check you privilege" is the common campus shorthand nowadays for "shut up white male." Males, whites, the religious, the well off -- these are the new out-groups whose origins are used to automatically invalidate anything they say.