Here is a sort of thought experiment:
Let us say there is a secret prison bunker in an unmarked, uninhabited island far from a main continent. There are two prisoners in a cell: one a militant atheist and one a very devout fundamentalist Christian. They do have something in common though: they are both absolutely convinced, without doubt, that they will never be found, and that they will die in the cell. Let us also assume that they have food, water, and medical all provided for.
This is my argument:
It is the Christian's duty, from above, to convert the atheist to theism in order to save his soul so that the atheist can experience eternal paradise. The atheist, on the other hand, does not have such duty.
The reason the atheist does not have such duty is because the Christian is simply an individual, and under materialism/naturalism, the individual does not matter. The only reason the atheist converts an individual to atheism is so that the individual will in turn convert other individuals to atheism and so on.
Conclusion: what matters to the atheist then is not the individual but affecting society so that society is more fit to the liking of the atheist. Therefore, the atheist is using the individual as a means to an end while under theism, the individual is primarily and foremost the end.