Excellent point, Obadiah! It is never a sin to stop a crime. I believe the crime (sin) is exactly what Scripture says it is: to know to do good, but don't.Has anyone yet considered that in self defense, even using a gun, that your goal should be to stop the act of violence the other person is committing rather than your goal being to kill the other person? Even with a gun, if it is the last resort, you still don't have to have the mindset that you are out to kill someone, just that you have to stop them and this is the last option available to you other than just letting them get away with what they are doing and probably kill you or someone else. Yes, shooting them may kill them, but many times it doesn't. When you're full of adrenaline you really aren't going to place that bullet right between their eyes like they do in the movies. Just ask anyone who has been in a real life situation where they have actually had to shoot someone! Even if you've had training and practice you'll probably be lucky to hit them anywhere at all! So if your mindset is right, killing the person isn't your goal. Stopping the crime is your goal, and if that results in their death, that's just a sad reality but it didn't have to be your intention. How is it a sin to do what you can to stop someone from committing a violent crime against you or against someone else?
James 4:17 - Therefore to him that knoweth to do good, and doeth it not, to him it is sin.
To not protect one's loved ones is akin to being "worse than an unbeliever".
1 Tim 5:8 - But if any provide not for his own, and specially for those of his own house, he hath denied the faith, and is worse than an infidel (unbeliever).