Matthew Stewart, Nature’s God: The Heretical Origins of the American Republic (W.W. Norton & Co., 2014), 427.
To attempt to explain the world today through the categories of the common religious consciousness is to live in a kind of moral chaos. It is to inhabit a house of fractured mirrors, where submission to inscrutable authorities counts as freedom, where that which is good for the health of the individual and the collective is called evil, and where all are expected to bear the lifelong burden of pretending to believe one thing while doing another. Once upon a time, it took a certain kind of genius to see that atheists could be virtuous. Today, only those blinded by bigotry can think otherwise. The revolutionaries of the early modern period needed their books to imagine a world free from the chains of the common religious consciousness. Today we need only our eyes.
The Amateur Exegete 
Building off the passage above, I would point toward Thomas Paine as a good example of an early example in the United States of a free-thinker with both a strong moral “compass” and passion for his fellow humans. He participated in both the American Revolution and French Revolutions (later rejecting the violent methods of the Jacobins) while being demonized, partly for his professed deism and partly for his resentment at serving time in the Bastille.
Paine certainly had his faults but can also be given credit for opposing slavery in an era where so many prominent figures (including several of the Founding Fathers) either tolerated it or had slaves themselves. And you can’t help but find his expressed desire to free mankind from what he saw as tyranny to be a refreshing “mission statement” in a secular society.
He probably wasn’t an atheist (at least according to his Age of Reason) but still provides an illustration of how the non-Christian can behave just as morally and with as much conviction as their church-going counterpart.
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