This is an awesome thread. Thank you for starting it, whoever that was.
I've noticed a lot of comments answering the subject question with something like "Because I live in [XYZ City/State], that's why," or "Because I can," which is OK but sorta misses the point. I think some folks have confused this thread with a "Why do you CCW?" type thread.
If any of you have done that but actually did have a Defining Moment at some time, I invite you to Edit that into your original post. I don't know about you, but I've used anecdotes from this thread in conversations with others on numerous occasions.
So keep 'em coming!