I think, sociologically speaking, it is a bit narrow-minded to try and understand complex socio-political happenings by emphasizing religiosity and irreligiosity. I think it is much more sensible to emphasize the environmental, social, and economic conditions. While religious affiliation surely reflects this, it can hardly be said with any seriousness, to drive it. You seem to strawman secularists by saying that they all believe human beings are "nice and peachy". I don't think anyone believes that. What they do deny is an event of original sin that leave human beings inherently corrupt. Denying that isn't denying humans do awful things or that the world isn't Utopian. Rather, it is denying there is no supernatural, metaphysical grounding for such atrocity. To quote Richard Lewotin, it just "isn't in our genes". Humans are not predisposed to do evil things. There are plenty of ways to cultivate virtue through reorganizing the way we socialize, the way we economize, and the way we politicize. As Stephen Jay Gould remarked,

"There are no shortcuts to moral insight. Nature is not intrinsically anything that can offer comfort or solace in human terms – if only because our species is such an insignificant latecomer in a world not constructed for us. So much the better. The answers to moral dilemmas are not lying out there, waiting to be discovered. They reside, like the kingdom of God, within us – the most difficult and inaccessible spot for any discovery or consensus".

Secularists are not mere utopians; they think we are good enough. Rather than heading the words of God or prophets, they think that taking seriously the words of sociologists and anthropologists who have given clues on how one ought might go about organizing a just and equal society.

Secularism is not a descriptive, deluded description of our current life. It is a prescriptive program challenging the typical Western conception of human nature by envisioning societies built on cooperation, mutual aid, and solidarity between people, rather than competition and survival of the fittest. It is the belief that humans are flexible beings that have no inherent nature besides what is reflected through socialization. This seems not to be wishful thinking, as we are quite aware of many egalitarian socialg groups, whose way of living cultivated virtue and discouraged vice — free of oppression and coercion.