If Hitchen's challenge is correct, then why are there ethical lapses?

[pokoko]

Looks like others have already beaten me to the punch, but I'll say it anyway: why do Christians sin when they're told in definitive terms what is right and what is wrong?

Because human beings are fallible and influenced by many divergent factors. You know this already, I'm sure. In fact, Christianity hinges on this idea to a large degree.