Probably because you're an imbecile that cannot convey sarcasm correctly due to your inability to differentiate between an exclamatory statement and a question.
... Y'know, if you object to the way someone said something, that's fine. If someone insulted you directly, or someone else directly, you would be more than justified in attack them. But calling someone an imbecile because they attempted to convey sarcasm in a text based communication, in which inflection doesn't carry? You've got some serious issues, my friend.
Granted, you springing to the defense of someone else is admirable, kudos to you for that, more people need to behave like that. But you went a BIT too far with the direct insults, when none were thrown out prior to your intervention.
You insulted his intelligence with your sarcasm, which was uncalled for. Therefore, I took it upon myself to do the same or, rather, take it to the next level (subjective). Granted, I was splitting hairs and I do agree that inflection does not transition well to electronic communication, but there is certainly a difference with the manner that one might read it (again, splitting hairs).
However, that insignificant reason aside, it was mostly my attempt at humor.