Why, lily? Why would being better at being religious make people better, on average, than not being religious?
My argument is that although any particular religious person (of whatever religious faith) might make someone a better person in one or more ways than any particular non-religious person, the reverse also applies equally, and therefore, on average, over a large enough random sample, there will be no evidence to suggest that being religious makes people better, on average, than non-religious people, and vice versa.
I'm not saying here that not being religious is an advantage either in making people good or not good. I'm saying it doesn't make a scrap of difference because goodness comes from all parts of life, not just religious parts.