Think it through deeply before you carry.
You need to make that moral decision before you are faced with the situation.
Think about and understand, "internalize", as the catchword goes. Know fully that you believe you would be justified in killing to protect your life or the life of another innocent. Think, also, how you would view yourself if you didn't...if you stood by and an innocent was killed and you could have prevented it.
If after all that consideration, you do not know for sure you would be morally (to yourself) justified, I'd say don't carry.
Also note that even if you have made the decision that you would be morally justified in a self defense killing, you still don't know what you will do when it's time to pull the trigger....not for sure.
But I do believe that the more you look at it and consider all the "angles" the more likely you will be to do what you have thought out to be right when the time comes.
About negligent discharges. They can be avoided by never being negligent.
If you don't know the 4 rules of safe gun handling, learn them and every time your fingers touch your weapon, be thinking of them.
When you have your gun in your hand, it needs to be the center of your attention..along with your target if you have one. Just never be casual with it. Treat it like a running chainsaw....be aware of every move you make with it.
Good luck and take care.