You are right about atheists who demand their Constitutional Rights, but refuse to acknowleged, as our Founders exresssly did, that God is the Source of these and all human rights. Atheists have been writing checks on the moral bank account of Christianity for ages, all the while mocking the very concept of a God, without Whom all moral reasoning may be reduced to a matter of arbitrary and temporary human arrangements, or personal preference.
The notion of moral/political systems as merely the transitory expressions of various groupings of human interest (i.e. classes) is what underlies Marxism and its academically fraudulent cousin, Deconstructionism. And it is what leads to class warfare and justifies the power-driven intellectuals in mass-murder and totalitarian repression once they gain power. Ideals not tempered by the recognition of a Creator become a carte blanche for terrorizing your opponents into submission. If this country had been founded on an expressly atheistic or agnostic creed, I have no doubt it would have fallen apart within a decade or two. Thank God it was not, and did not. Nor will it.