Jeremy Waldron is probably the foremost authority on the need to give human rights a theological grounding. This paper explores issues with using "Imago Dei" to ground human rights.
Second, there are questions about what imago Dei means in the light of doctrine of the fall into sin. What is the relation between imago Dei and our fallen sinful nature? What can human rights theory do with Calvin’s doctrine that the image of God in us is now but a “relic” or Martin Luther’s teaching that since the Fall we are more “like” the devil than “like” or “in the image of” God? When we use this doctrine in the context of human rights, are we committing ourselves to saying that Luther and Calvin were wrong?
It's surprising how many otherwise informed and intelligent folks are so quick to conflate their theological desires with America's Founding Fathers. The syllogism works something like this:
1. The Bible/Christian Religion/Calvinism is true;
2. Therefore I am a reformed Protestant in that sense;
3. The American Founding was a great event, one in which I'd like to believe my personal religious tradition gave us;
4. Therefore, the political-theological basis for the American Founding must have been the same as Calvinism (or whatever my religion is).
This syllogism works with anyone's personal religion. Though the further one's personal religion from that of the actual American Founding, the more of a stretch it becomes.
For instance, beginning with "Hinduism is true" results in an especially absurd syllogism. But ultimately, the entire syllogism, no matter what one begins with is an error. As I've said before, the political theology of the American Founding offers a little for everyone (including the Hindus!) and a little for no one.
If one doesn't take one's personal religion that seriously, the syllogism seems a harmless error. The more seriously one takes one's religion and values it over politics, the more dangerous the syllogism. America's Founders could have been wrong on how they understood theology and how it ought to apply to politics. If they were wrong on Romans 13 (which there is good reason to believe, from a strict literal textual interpretation, they were) the Bible says, "they that resist shall receive to themselves damnation."
It's only your soul that is on the line. Don't let America's Founders, and your desire to claim them, confuse you into making a soul damning error.