True or useful ideas certainly have a selective advantage insofar as humans care about usefulness (I'm going to go out on a limb and just say outright that humans don't care about truth), but there can be other features of an idea that convey a selective advantage in memetic competition; for example, an appeal to alleged consequences of accepting the idea. This is the reason so many religions prominently feature promises and threats of divine reward or punishment: "Believe X and you'll be rewarded; believe not-X and you'll be sorry" is _more memetically fit_ than "It happens to be the case that X, but this has no particular further implications," because the former creates incentives for propogating itself that the latter does not. It doesn't _matter_ that the rewards and punishments don't actually exist—
True or useful ideas certainly have a selective advantage insofar as humans care about usefulness (I'm going to go out on a limb and just say outright that humans don't care about truth), but there can be other features of an idea that convey a selective advantage in memetic competition; for example, an appeal to alleged consequences of accepting the idea. This is the reason so many religions prominently feature promises and threats of divine reward or punishment: "Believe X and you'll be rewarded; believe not-X and you'll be sorry" is _more memetically fit_ than "It happens to be the case that X, but this has no particular further implications," because the former creates incentives for propogating itself that the latter does not. It doesn't _matter_ that the rewards and punishments don't actually exist—