It seems very
self-explanatory to say this, but it seems to be a rule that many people, both on
everything and in
real life, don't understand.
Disagreements are fine. People differ in what they believe, what convinces them, what they hold to be true, even what things they take on blind faith. Hell, disagreements are what life thrives upon. People have to hold diffent ideas, and they should discuss them. The world changes because of exchange of ideas, especially an exchange of different ideas. Preaching to the choir doesn't do a whole lot of good, does it?
However, disagreements can be lively and passionate without being insulting. Saying "While I still respect you, I still disagree with what you are saying" is very different from "You're a moron. You don't deserve to use up valuable oxygen to feed that stupidity." Personal attacks are not something that have any place in a disagreement and do a whole lot more harm than good.
Trust me, if you want me to listen, the least effective way to do that is to insult me.
Discussions can happen without insulting or derogatory things being said. Hell, discussions SHOULD happen without these things ... we're all adults here, right? Then let's prove it.