Listen before speaking. Be willing to let another person change your opinion.

If you're only here to enforce your opinion, then don't talk about the topic. This is why religion and politics are usually not welcome in most parts.

There was an opinionated conversation on anarchy philosophy a few weeks ago on front page HN. Most of the comments came from people who obviously did not open the link at all. Some from people who copied snippets out of context to attack.

This happens because they were not planning to have a conversation. They were not open to the idea that anarchy could be superior to democracy. It's fine to hold firm opinions, but pointless going into discussions with them.