Eliezer jumps from the ostensible purpose of churches to the claim that they are not optimized for community. The ostensible purpose doesn't tell us much! Churches look to me to have a lot of optimization for community.

I do not claim that churches are optimal but I doubt it is as easy to improve on them as Eliezer implies. The very items he points to look to me to be powerful rituals. Maybe those rituals serve some purpose (eg, brainwashing) other than community, but it is important to understand the data we have about organizing humans. Communities are slow and expensive experimental subjects.