I normally don’t feel personally attacked by someone disagreeing with my point of view. I actually welcome debate. I enjoy it when someone changes my view or helps me see things from a different perspective.
However, I am only human after all and there are a few people who have managed to get me into a slightly irritated state and I become more likely to attack the character of the poster verses the points they are trying to make. Although I still address the points I tend to focus more on the poster in that situation.
But overall in a ideal world, I focus on the subject at hand and give my point of view and opinion as level headed and informative as I can.