The non-aggression axiom is the fundamental principle of classical liberalism:
It is illicit to initiate or threaten invasive violence against a man or his legitimately owned property.
There are only two types of rights, and they are covered by this axiom: personal rights and property rights. Those two rights cover everything so, for example, there is no such thing as “human rights” or a “right to free speech” (they are in fact dangerous fallacies), and I have explained that in this post.
Every issue should be considered in light of this axiom, and every solution should comply with this axiom.