I carry a gun because the Safety of my wife, and 6 month old daughter are far more important than any guilt I might feel in association with doing what could be necessary to protect them.
The guilt of taking a life in defense of myself or family could only be beaten by the guilt of losing one or both of them because I was unprepared or unwilling to do what had to be done.
I carry a gun because the world we live in is a nasty place where bad things happen to good people. I like to be in control of my fate to whatever extent possible.
I carry a gun because it makes me look like a really tough guy.
Also because I can't morally ask any other human to put themselves into a life-threatening situation in order to get me out. Because, given the vastness of Earth and the fullness of time, I can't logically expect there to be someone around to help me in the few seconds it takes to get mugged, beaten, or killed. And finally because there really are evil people on this world and I won't leave the lives of my family and loved ones up to someone else's mood.
1st and foremost, because we have the right to bear arms. 2nd by doing so you are supporting that right. Even though you may not display it, you still support it. 3rd this country is not perfect. Crime happens every day. It's keeps getting worse, and is going to continue to get worse. I'm not going to intentionally let myself, my family, or my friends be victims.
I carry a gun because I cannot depend on anyone else to protect my family and myself.
In all of the "person attacked" news stories we see every day, how many involve a 3rd party (cop or civilian) who successfuly jumped in and saved the day? So few that I only remember a handful in my whole life. Yet, we always see the sad news stories where an innocent person was either injured or killed.
If I want to have a chance defending my family or myself I must have the tools and the means. As the old saying goes, "chance favors the prepared".