It has nothing to do with what anyone "decided." It was people who believed our inherent rights are not granted by man.
They didn't establish a Christian theocracy. The 10 Commandments were not written as the basis for establishing a government, they were written long before the founding fathers as a means to lead a people out of bondage to a better life. If there is any intrinsic connection to the Constitution, it is that American Exceptionalism is the manifest realization of the same dream, for people to be removed from the bondage of tyranny to govern themselves and live a better life.
It has nothing to do with a religious belief of what a "creator" may or may not have "said" to followers, it's about mankind's universal rights we are born with as humans, given to us by whatever 'God' we believe Created us. We don't have to agree on the Creator, or accept the same incarnation, this has nothing to do with that, because it is clearly stipulated in the First Amendment this is not the case.
Again, The People didn't "decide" on the rights. They are there, regardless of people's decisions. That was the whole point... The King of England "decided" our rights for us, and we didn't like it. We established a nation, a constitution and a government on the basis of endowed rights, not "granted" by man.
Self-evident means, it should be evident to anyone who isn't a simple-minded idiot. And they didn't hold that the "rights" were self-evident, they held the "truth" was self-evident. The truth being, that all men are born with natural rights endowed by the Creator. So they say... The TRUTH... is apparent, even a stupid idiot like Apple can see this... our rights don't come from a King or a Court, they come from our Creator and endowed to us at birth as humans.