Historically, it's the other way around. There were morals and philosophy long before the Christians made it part of their religion. Yes, there was belief in powerful, capricious gods - but that concept was quite different from the Judaic god. Alexander of Macedon decided he was a god for some legalistic purposes - he certainly fit the 'more powerful than normal people' profile - and that's what he meant.
Just because the Judaic/Christian/Islamic god is out of the picture doesn't invalidate any of the philosophy that came before - and there's no reason for it to be dark.
I find my views best match up with Epicurus: there may or may not be gods, but if there are, the're on such a different plane that they don’t care what people do. And after death is just like before birth - no painful existence as a 'shade'. He had many followers before Christianity (based on epigraphs on burials; early Christians did their best to obscure his teachings, turn him into the 'eat, drink, pleasure' guy as they were fanatics doing bad things (e.g. burning library at Alexandria). They were mostly successful as velum doesn't last that long and recopying manuscripts was done at monasteries - and many of the ms at that library were single copies, so nothing to copy anyway. Most of what's left is in quotes in other works.
No links; I'm on a mobile with spotty coverage...