I like to employ a somewhat Hazlittian-utilitarian basis for rights. I’ve read Foundations of Morality, and Hazlitt didn’t really touch on it in there (though perhaps he did in some other works), but my thinking seems along the same lines Hazlitt followed in FoM:
A right (noun) refers to a claim that is at all times morally right (adjective) for an individual to make in regards to himself and the action of others toward himself. What is right or wrong refers to nothing other than what is the right or wrong means to employ in order to achieve a desired end. The end that all humans seek (knowingly or unknowingly, stupid or smart, sane or insane, masochistic or selfish, etc.) is the maximization of personal satisfaction and well-being. Every human’s goal is to always substitute a more satisfactory state of affairs for a less satisfactory one, and thus, as follows, to achieve the most satisfactory state of affairs that they possibly can. So a right can be thought of as a claim, or a principle, or a general rule of action, that an individual can make at all times, that will, logically, lead to the maximization of his own personal satisfaction and well-being. A natural right is nothing other than such a right that is inherent in every man’s nature, not just what is right for one particular individual, based on one’s preferences or circumstances.
So in judging what should be considered a natural right, one must merely find out, rationally, what is the right means (the right rules of action) for every man to employ to achieve the end that every man seeks (maximization of personal happiness).
You can get to the root of it here by establishing the rule of self-ownership. Ownership means the exclusive right to keep, use, be responsible for, and dispose of a certain thing. So who has the exclusive right to keep, use, and dispose of a certain thing? (Here is where Rothbard’s “Ethics of Liberty” comes in handy) There are only four options: You own yourself, some people own other people, everyone owns everyone, or no one owns anyone.
Some people owning other people can never, logically, succeed. This is because each individual has a massively complex, intricate, and nuanced system of values, of what they value, of what gives them more satisfaction or less, of what their individual wants and needs are. Therefore, on the whole, other people can never make better decisions for other people than each individual can make for himself. It’s purely common sense logic. So, some people owning other people is not the the right means to employ to achieve the universal end we seek (maximization of personal happiness).
Everyone owning everyone, by its very nature, is destined to collapse, since we can’t keep continual tabs on everyone else at the same time. Inevitably, the division of labor will find one group of people that are “good” at “managing” others and will specialize in it, while the rest of the people who aren’t as skilled or enthusiastic at that task leave it to the special managers. In other words, everyone owns everyone is destined to collapse into some people own some people. Therefore, it cannot be the right means to employ to achieve the universal end.
No one owns anyone (what those who say that there is no objective morality, and that morals are just a ‘social construct,’ would imply) does not give others the right to keep, use, be responsible for, or dispose of others, but it does not give you the right to keep, use, be responsible for, or dispose of yourself either. In this case, society is destined to become a free for all. Might makes right. Whoever can grab the most, wins. The practical flaw in this claim is so glaringly obvious that no one really accepts it, even if they say they do. Needless to say, no one owns anyone cannot be the right means to employ to achieve the universal end.
Only “you own yourself,” or “self ownership,” can be a universal right. In other words, each individual claiming the exclusive authority to keep, use, be responsible for, and dispose of their selves, is the most efficient way for each individual to achieve the end that they all seek (maximizing personal happiness, or achieving the most satisfactory state of affairs they possibly can), and so, since self-ownership is the right means to employ to achieve the end that all humans seek, therefore self-ownership is, according to our definition, a natural right. It is a claim that it is right for every individual to make, and it is a claim that can be derived from inherent human nature.
This post is already getting lengthy, but it’s much easier to establish the rest of the moral principles once you establish the right of self-ownership.