Reactivity and being defensive

....CODEPENDENCY...I must say I wasn't fully aware of how it effects my life and situation until I read this article. http://psychcentral.com/lib/symptoms-of-codependency/
One "symptom" I'm dealing with today is Reactivity. "Reactivity. A consequence of poor boundaries is that you react to everyone’s thoughts and feelings. If someone says something you disagree with, you either believe it or become defensive. You absorb their words, because there’s no boundary. With a boundary, you’d realize it was just their opinion and not a reflection of you and not feel threatened by disagreements."
I find myself getting very angry almost immediately when someone posts something I find negative toward me. This happened today (on another site). I posted about someone dealing with HOCD issues. I learned what HOCD meant today (Homosexual Obsessive Compulsive Disorder). I was corrected and "should be careful what I say doesn't send someone into a spiral". I didn't say anything aggressive or negative in any way. I was simply stating my experience and others felt I shouldn't say anything because I don't the disorder. I feel angry just typing this. I have trouble knowing when to speak up and defend myself and when to let it go....(I almost never let it go). I responded to the post I felt was attacking me for posting. Maybe I shouldn't have even done that. I want to go back there right now and give them a piece of my mind.
 
This isn't the first time I have gotten angry over an Internet comment (or ambush), posted my mind, and end up being the bad guy. My husband always points out that I take it too far and end up being the bad guy. WHY do I care so much? I have issues....