My personal ethics are based on the libertarian "non-aggression principle," in other words, don't violate the rights of other persons,

You're describing a deontological branch of ethics, I think.

As for virtue ethics, I believe virtue ethicists evaluate the morality of a deed based on whether it ennobles or debases the doer. In short, "charity is good" because it instills to you habits of charity that makes you a better person. But perhaps a virtue ethicist would be better fit to explain it (and my apologies to them if I got it wrong).