"but, science says the purpose of existence is to maximize your number of descendants, so shouldn't being an atheist mean you want to have as many kids as you can?"

it's funny how religious people tend to think that science perfectly upholds religion, isn't it? i mean, how could it not, if you're absolutely certain in your faith? that's the thing about faith - all possible evidence always upholds it. if you have faith in santa claus, the absence of presents under the tree any given year just proves you were bad. and, if you have faith in god, then any possible set of events that can be thrown at you will just be perverted to offer more and more evidence for it's existence.

faith is a perversion of logic. that is why it is such a dangerous tool, and must be kept away from the state.

in the western/judaic context, this talk of descendant maximization goes all the way back to the torah. god gave abraham this purpose. but, how did this get attached to science? well, it didn't, except in the minds of religious people, that are seeking out some kind of purpose, because that was what they were taught to seek out.

so, we have this problem: when people raised with religious upbringings come into contact with science, they need to frame it in terms that they understand. religion teaches them that existence is about purpose, and that that purpose has something to do with god (although this itself is circular logic, as the purpose is created to justify god, rather than the other way around). if science is to offer some alternative to religion, it must offer some alternate purpose, right? and, from there, they come up with this vulgar dawkinsianism that deduces that our purpose, as humans, is in carrying on the dna. we exist to breed.

but, the reality is that you'd be hard-pressed to find a scientist (or an atheist) of any ability or renown that would accept that humans have any kind of purpose, as that pre-supposes that a god exists to define it, first. who or what defines purpose, if god does not exist? it's a neat trick that the religious person does, here, in defining existence in purely religious terms, before bringing it to the scientific bodies for answers, as, once you have done that, you have hard-wired religion into the question, and made it useless to science. you can walk down this path with philosophy, it's what it's all about, but not with science, which will provide you with no worthwhile answers if you present it with what are brutally leading questions.

science cannot pre-suppose that a purpose exists. science must gather evidence to determine if it suggests that a purpose exists. whether the nature of the purpose is an empirical question or not, which is what the religionists pre-suppose and assign to scientists as a strawman, is reliant on whether the purpose exists or not, first, which is also an empirical question, and not something to pre-suppose at all.

while it would be extremely difficult to do a comprehensive study that empirically disproves that we have purposes, the lack of evidence underlying any purpose is a convincing argument that we have no purposes, for most atheists and most scientists.

and, so this is what the atheist will tell you: science does not argue that our purpose is to breed, but rather that we have no inherent purpose at all, and are free to define our purposes as we see fit to do so.

i've decided that my purpose is not to raise a family but to to complete my discography, and, because i seek to be free, there is nothing in the universe that has the right to challenge my authority on the point.