It would be really convenient if rationality, the meme-cluster that we most enjoy and are best-equipped to participate in, also happened to be the best for winning at life.

As I've seen it used here, "rationality" most commonly refers to "the best [memecluster] for winning at life" whatever that actual memecluster may be. If it could be shown that believing in the christian god uniformly improved or did not affect every aspect of believers lives regardless of any other beliefs held, I think a majority of lesswrongers would take every effort necessary to actually believe in a christian god. The problem seems to be how rationality and "the meme-cluster that we most enjoy and are best-equipped to participate in" are equated- these two are currently very similar memeclusters for the current lesswrong demographic, but they are not necessarily so. "It would be really convenient if the meme-cluster that we most enjoy and are best-equipped to participate in, also happened to be the best for winning at life, rationality." seems more sensical.