In one debate Christopher said:
We don't say on non-truth claims or faith claims that we know when we don't.....atheists do not say that we know there is no god. We say to the contrary, no argument and no evidence has ever been educed that we consider to be persuasive......The same with the afterlife. Of course we don't say that we know there isn't one. We say that we don't know anyone who can bring any reason to think that there is.
This is an important distinction that atheists must be aware of because we cannot let ourselves become as arrogant as those who say they are certain god and the afterlife do exist. I agree with Hitchens that the atheist position should be one that affirms that no human has ever made a convincing argument or introduced convincing evidence that god exists, and until someone does, it is just another person's matter of opinion.
Now I am aware that there are many theists who also do not say that they know god exists and instead lay claim to a probability tilted in favor that god does exist. I'm fine with that, and I prefer the theist who takes this position over the one who is absolutely certain.
Atheists are skeptics, it's in our nature. As far back as I can remember, I was questioning the truthfulness of claims made by theists. Knowing this, it is important that we apply our skepticism where ever the lack of certainty without empirical evidence exists.