There are two arguments for the non-aggression principle:
1. Violating the NAP has bad consequences.
2. Violating the NAP is immoral.
Since I'm not a consequentialist, I don't find the consequentialist argument convincing one way or the other.
As for the argument from morality, all moral claims are opinions. They are preferences, nothing more. You can't say my opinion is wrong any more than I can say yours is wrong. That's because opinions aren't the kinds of things that can be right or wrong. That being said, I reject any opinion that violating the NAP is moral, outside of immediate life threatening situations when your actions don't threaten the life of another person and you also compensate the victim. If you are literally about to starve to death, steal some bread but be prepared to work it off. I doubt you'll have to steal though because I'll be glad to give you some of my bread. However, if you are dying because of liver failure, don't take my liver.
If you reject my opinion like I reject the opinions of those that wish to violate the NAP, we have irreconcilable differences. We can either try to coexist peacefully or we can go to war. There's nothing more to it than that.
NOTE: Any posts that are not a direct reply to this argument and attempt a direct refutation of it will be deleted.