I found a wonderful series of videos describing morality and secular thought. The argument made is in a series, from the first video talking about how one can be moral without a god.
In the videos that come after, it is described how morality based on ancient religions is often flawed, and then described a secular base for morality.
The crux of the argument of secular morality is summarized pretty early:
“If two humans perform an action, one thinking its evil, the other having no sense that its evil, what they believe about their behavior is irrelevant to our moral assessment.”
If someone is ignorant of their act being ‘evil’, we don’t consider what they did evil, but can still call it morally wrong. To put it simply, ‘evil’ is in the eye of the beholder. Which means that any ‘objective acts of evil’ will also be in the eyes of the beholder.
Relative morality is often a problem for those coming from religion and entering a secular world, but getting over that hump is a quick way to understanding your neighborhood atheist.