I remember seeking Christopher Hitchens bring up a challenge to Christians in a debate:
Name one moral or ethical action or behaviour committed or carried out by a believer that could not have been committed or carried out by an atheist.
So, then the conclusion from this challenge (I am taking the first part) is that an atheist can live a completely moral life without God. Well, if that is the case, then why are there ethical lapses? If it is simple for man in and of himself to end up doing what is right, then why do people have ethical lapses? And, I would have to ask then here: Does anyone know anyone personally, or themself, who could end up saying honestly that they never had any moral lapses? In short, how many sinless people do you know of?
If Hitchen's challenge is that simple to do, then why does it seem to fail so much?
The second half has to do with doing evil in the name of God.