economically, i'm about as free-market/libertarian a person as you're likely to find, but the survival of the fittest idea (in any arena) has its limitations. look at the the new york times bestseller list, the top grossing movies, fashion, album sales... are these the best representatives of their form or the most easily consumed?
think of mcdonald's... sure they're the "fittest" in a way. they deliver an easily consumed product at a rock-bottom price with speed/convenience. few would argue that they aren't popular, but how does that translate into intrinsic worth?
as for getting along well without it,
85.8% percent of people in the US describe themselves as identifying with some religion. if you're thinking we're getting along well, then it isn't because we're doing without religion.