I'm not entirely sure what you think isn't offensive about your comment.

1. You are responding to the comment "Since when has it become fashionable to define oneself by religion?" (aside: the answer is since forever) in the affirmative

2. You find it "interesting" that "clearly rational and intelligent people have faith", by which you say that most people who have faith (and by association, Christians) are irrational and stupid.

3. You say that you believe that you expect those who have faith must be seriously uneducated.

4. You say that people who have faith use it as a crutch.

Hope this helps.