In my political wanderings, I've learned several lessons. They usually have something to do with remembering that the other person in the debate is a person, too.
My wife's best friend has a nephew who served a mission for the LDS church, and, upon returning, announced that he was homosexual. Another uncle promptly announced that his family--particularly his sons--would from henceforth have nothing to do with the nephew. Irrational fear makes us do irrational things. That's how not to treat people.
As told on PBS "The Mormons", a woman who had been excommunicated from the LDS Church was not allowed out of spite by her brother-in-law to be present when her sister (his wife) was clothed (in LDS temple clothing) for burial. That's how not to treat people.
Several years ago, I was talking on the telephone with my teenage sister. She told me of something she had done that she was not particularly proud of, upon which I piled on the criticism. She already had had enough of that from herself. She said, "If you're going to talk like that, I just won't talk to you anymore." She was right. It was then I learned that that's how not to treat people.
I was a member of a city council in Utah county for a bit over 5 years before I was called to military service in Iraq. Over the course of that time I saw a litany of examples of how not to treat people. It reminded me of when my father had served several years prior on both the city council and as mayor in a small southern Utah town. He was an example of nobility and decorum as he avoided the ad hominem attacks that other council members and the public often engaged in. People later came to him and apologized for their actions and thanked him for his. I can say that in my time as a city council member I made my father proud, because (despite witnessing it frequently in others) I have no instances where I can look back personally and say "I shouldn't have treated him or her like that."
Life is to short to treat other people like dirt. If someone disagrees with you, I suggest you decide that they must have a good reason for it. Then I challenge you to find out what that reason is. In nearly every case, I have found, you will be glad you did, because you'll find out that they did have a good reason.
That's how to treat people.