We Hold These Truths To Be Self-Evident
Human nature being understood, and moral language being understood, one can make some observations.
Human beings are more likely to thrive under conditions of liberty. The chances of fulfilling a person's preferences by coercing him are much lower than his own chances of fulfilling his preferences by his own discovery of those preferences, decision as to how to fulfill them, and freely undertaking to act on his decisions. If his betters have wisdom on the matter he can seek it out by inquiring of them. If someone decides to control and coerce him, it will unlikely be his better and even if it is, it will unlikely be a man who could fulfill the preferences of his subjects as well as they could fulfill their preferences.
This is pretty close to self-evident. Anyone who understands human nature and history sees that this is so. This is part of the reason why it makes sense to say that it is self-evident that we are endowed by our creator with certain inalienable rights.
The rest of the story is this. The terms of morality, "right," "just," "good," and so forth are defined in such a way that certain truths are self-evident, tautologies. "People have a right to the property they earn by labor." "People have a right to liberty." "People have a right to life." Also, "men are equal" in the sense that they are equal under the moral law is true because this is simply the statement that different moral evaluations require that there be relevant differences between the subjects of these different evaluations. If we judge person A's action to be permissible while person B's we judge to be impermissible, then we must be able to point to a morally relevant difference between their actions. In other words the concept of the moral law entails that all subject to it are equal under it. These truths are self-evident because there is nothing that would count as evidence that they were not truths. They are momentous tautologies subsisting at the core of the conceptual system of morality. Morality isn't about cheese or planets. It is about these things; they are the warp and woof of it.
This is why it is so that "we hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness."