I never had a defining moment, more of a natural progression. Most of my family are LEOs, lawyers or something in between, and on top of that my grandfather is a hunter. Guns, and their safe use, has been instilled in me since I was a small child.
When if came to picking my major in college, I choose criminal justice. The combination of my fathers police work, two shootings, and the information I acquired in school, led me to realize you can have the best police force in the world, but that doesn't matter much if you are sitting at a stop light and are getting car jacked. The response time will never be quick enough to help you. I choose not to be at the mercy of someone elses protection.
This has been further reenforced by recently becoming an uncle. I dont even have kids of my own, but I know I would do anything to protect my nephew.