God Given Rights?

I want to journey back towards the topic of god for a moment, since I've strayed from it in recent posts. I read an article recently in the Washington Post that was linked on the Nonbeliever Nation Facebook page, about secular and atheist organization's attempt to lobby Washington on behalf of atheists. The author, trying to be humorous, poked fun at the irony he saw where the atheists were using their "God-given rights" to petition their government for a redress of grievances to exclude mentions of god on our money, in our pledge, and while taking an oath. Now I have to take issue (naturally) as an atheist, with the whole idea that our rights are god given by pointing out some obvious issues.

If our rights, as described in the Bill of Rights, are god given, then why aren't those same rights simply written in the bible? Why would it have taken thousands of years after god originally revealed himself to us for our rights to be inscribed into law? It would've done the world some great justice over the last few thousand years if we were to have outlined in the bible the universal freedoms that we Americans enjoy. Furthermore, why do the rights outlined in our founding texts differ from the rights outlined in the bible? Did the practice of slavery, that is completely condoned in the bible, only become wrong when the 13th amendment was passed outlawing it? If the bible is the word of god, and it contains what our rights and freedoms are, then the U.S. Constitution, the Declaration of Independence and the Bill of Rights, would be blasphemy.

It is well known that the texts in which the U.S. is founded on, were inspired at least in part, by many of the enlightenment philosophers before and during that time, such as Thomas Paine and John Locke, and that many of our founding fathers were weary of religion and its influences, and that's precisely why they created a secular government free of institutional religion at the federal level. So this idea that our rights were "given" by god is at best, an attempt to insert the hand of god where it is certainly not needed.