No, I don't think you do. They weren't equating rights to physical laws or anything like that. They were saying that rights don't come from kings. They were advocating a better society, not magic.
Actually, many of the founders did in fact believe in natural rights and were in fact advocating they be supported by the new government. Saying something like the man that finds the acorn in the woods has a rightful claim to it is advocating an ethical principle. Why would anyone else have a rightful claim to it? Because they want it?
Ask an actual slave if he disagrees with that sentiment.
I'd be willing to wager that actual slaves had a very real problem with being slaves.....even those whom were utterly uneducated and totally ignorant of any theory of rights probably had the distinct feeling of being treated contrary to what they felt they were entitled to.