You're not the only one, i have exactly the same problem
and it's annoying me so i am trying to work on it too.
As for why some of us act that way, i believe its the fear of being wrong. And maybe we believe that being wrong implies weakness. And that being weak means others will like us less, or will think less of us. So we try to defend our viewpoints, even if they're wrong.
This can be a problem, because often considering someone elses critique might be worth it to us (as long as it is stated in a reasonable tone and reflects the truth)
Sometimes it seems like you just have to take a deep breath and re-evaluate the situation before you act, and then consciously decide how to act on it. At least with the blog you can take your time with your active response - e.g. you responding to the commenter - while it's a bit harder in eye to eye discussions.
The more often you make yourself consciously aware of your response BEFORE you communicate it the easier it gets until it, one day, it will hopefully become a habit. I know i am getting better at it, although i still fail more often than not
PS: What helps a bit is if you imagine that someone you dont mind getting critique from is voicing it. If there isnt such a person then imagine the critique is your own thought! Hey ... look at that , second post on these boards and i am already telling people to talk to themselves
