Well - it is my girlfriend who said it. I think the primary damage done by religion to atheists is the propagation of such things as "No one can possibly know" (which even some atheists unthinkingly repeat), a general tradition of avoiding the subject, an idea that you can say anything you want, and the contamination-by-association of any possible trick for living on after you stop by breathing.

The question you want is: in a world where religion had never existed, but people's reasoning abilities were otherwise mostly the same level, how many people would now be signed up for cryonics? This is the damage done by religion alone.