Atheists can be acting as morally, or more morally, as Christians. The only place the two meet is in the activism end which enrages many of us. But Christians also have their annoying activists.
To the point, some of these quotes are questionable.
I hold the precepts of Jesus as delivered by Himself, to be the most pure, benevolent and sublime which have ever been preached to man
I've never heard that one, although it could be possible withouth the capital on "Himself." The closest I can find is
To the corruptions of Christianity I am indeed opposed; but not to the genuine precepts of Jesus himself. I am a Christian, in the only sense he wished any one to be; sincerely attached to his doctrines, in preference to all others; ascribing to himself every human excellence; & believing he never claimed any other.He believed in the teachings of Jesus as a human, nothing more. Of course, anyone with half a brain and a good heart would find his teachings most wise. As to the mystical part of Jesus that your religion is founded on, Jefferson says about his teachings:
They have been still more disfigured by the corruptions of schismatising followers, who have found an interest in sophisticating & perverting the simple doctrines he taught by engrafting on them the mysticisms of a Grecian sophist [my emphasis], frittering them into subtleties, & obscuring them with jargon, until they have caused good men to reject the whole in disgust, & to view Jesus himself as an impostor.According to Jefferson, Christianity as practiced as a religion is a corruption of Jesus' works.
Many of the other Founding Father quotes can also be countered with others. But this more modern one leads me to a point:
President Ronald Reagan said, "Without God there is not virtue because there is no prompting of the conscience..."
This is a simple difference of worldview, nothing more. Christians see humans as highly fallible, needing the guidance of God to keep them in line. Your doctrine of original sin guarantees that we start out in a corrupted state, needing to be saved. Athiests, and especially Humanists, see humans in much better light, capable of being moral without daddy in the sky to threaten them if they get out of line.