This is the hypothesis that charitableness can be modeled on a normal distribution, but the additional incentive of religion shifts the mean of that distribution higher for religious people than atheists. It's not offensive to believe there is a subset of the population that is influenced by the dogma of the church to do things they wouldn't already do.

It's offensive to many, but it's also unquestionably true of a non-trivial portion of the religious populace. That subset of the religious demographic is also prone to making equally-offensive but less truthful accusations along the lines of saying that atheists cannot be moral because morality can only come from their god.