(a) refuse to let someone speak their own mind
(b) tell them that you know what they're going to say
(c) be condenscending to them based on your own assumptions
... yeah, you're off to a bad start.
But if you then allow others to be rude let's pretend someone is playing "telephone." and personally abusive That's a truly pathetic piece of weaseling to that person in comments in your LJ, what really are you trying to accomplish? You are *not* trying to have a reasoned, respectful conversation. You should not be surprised if that person withdraws from the conversation to avoid further abuse.
For my own part, I should never have bothered to follow up after this person originally started pretty much yelling at me (over his own misunderstandings) in person. I should have ignored the LJ post which was clearly trawling for more drama.
And yeah, in case you are wondering: If someone was personally offensive to someone else in a comment-thread I own, I would absolutely delete the offending post and send e-mail to both parties, apologizing to the victim and asking the aggressor to focus on the topic and not attack the person. This is basic politeness. That a fully grown adult can't handle that is shocking.