A single atheist can exist. A group of atheists, will argue theology until the cows come home.
Same with any other fundamentalist.
"Dude, aren't religious rules derived from the holy book/word of god?"
Somebody had to write that book. Long before it was in a book, it was oral tradition. Long before it was oral tradition, it was bedtime stories for kids by parents trying to impart wisdom to the next generation.
Most religions existed long before their scriptures were written. Scriptures are only necessary if you get more than four generations from the founder without the cult collapsing.
"Hunter/gatherers also needed a surplus before some voodoo priest can claim that his magically connection to God helped them find food."
Few hunter/gatherer societies ever achieved a surplus of food- every single day was spent hunting/gathering- and yet they still had priests (who were also hunters/gatherers, you're right as far as a priestly class goes, but the professional priest is a rather recent addition and even today isn't entirely true, every priest I know has side interests and side jobs).
We were better off then because we had the three noble virtues:
We were happier back then.
Slavery to lust is still slavery.