Just a few thoughts to add. As already pointed out, most communication is nonverbal, so this medium puts us all at a disadvantage when interpreting someone else's words on the screen. Until posters get to know each other a bit, it's only natural that we project ourselves, good and bad, into what we read. Then again, sometimes the other person really is over the line, huh.
Anyway, when another poster happens to push my buttons for some reason, my habit is to wait a bit before I reply. It might be a wait of a few minutes or even until the next day, but I know that if I post off the cuff, there's a good chance that I'll create unnecessary antagonism or fuel any bad feelings that already seem to exist. Sometimes, just to get it out of my system, I might write a reply to satisfy my offended side, but I never hit Submit. Later, when I'm calmer, I'll formulate my reply in a way that does get my point across but without creating undue tension on the board then send it instead. This is such a simple thing to do--the proverbial "first take those three deep breaths"--to keep disagreements from becoming personal that I, anyway, think it should be Rule #1 For Internet Discourse. The internet's not going anywhere, so there's always time to respond later without bad feelings that might be unjustified making things worse.
Another simple way to help keep peace on the board and conversations civil and on topic is merely to say, "I understand your point of view, but I disagree, and here's why..." No more, no less, and no "That's a really stupid thing to say, and you're stupid, too."

Have a great one!
Cindy