Religion is subject to natural selection just like anything else. Religions which produce more offspring that stay in the religion will always win out over the ones that don't.
> So long as the children survive to give birth to more children
Big if. In a true famine, the poor usually die first.
> Evolution doesn't care for the comfort of anyone.
Evolution cares about sexual desireability and fitness. Rich people usually have more.
In nature we see these two strategies as well. Some species try and have as many babies as possible, where others have fewer but concentrate resources to make sure the few are more likely to survive. Neither strategy is optimal in all situations.
You're mixing up personal fitness with the fitness of a meme. Sure rich people have more surviving children in the long run, but why don't we ask the rich Pagan Roman Senators how well their money protected them from the hungry Christian mob?