The Bill of Rights is itself based on natural law. Court decisions that respect the Bill of Rights are thus based on natural law.
The Bill of Rights and other human rights documents didn't actually create the rights that are listed therein. These documents simply list rights that people have already been given by nature. That doesn't mean these rights are always respected, but they ought to be.
We are commanded and expected by nature to enjoy these rights and strive for a society in which these rights are respected. This is a calling and a mandate that we all have.
Replace "nature" with "God", and you've got a Religious Right argument right there!
