At LW, religion is often used as a textbook example of irrationality. To some extent, this is correct. Belief in untestable supernatural is a textbook example of belief in belief and privileging the hypothesis.
However, religion is not only about belief in supernatural. A mainstream church that survives centuries must have a lot of instrumental rationality. It must provide solutions for everyday life. There are centuries of knowledge accumulated in these solutions. Mixed with a lot of irrationality, sure. Many religious people were pretty smart, for example Reverend Thomas Bayes, right? Also in my life I know religious people whose rationality is very high above average.
I am afraid that because of the halo effect we can miss a great source of rationality here. For example I am pretty sure that there are many successful anti-acrasia tactics written by religious authors. Another example: a list of capital sins, if you replace the religious terminology with something more lesswrongian, is simply a list of mental biases. (Pride = refusing to use an outside view. Gluttony = using a scarcity mindset in an abundance environment.) So I guess we could sometimes reuse the wheel instead of reinventing it.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
(I plan to make these threads from now on. Downvote if you disapprove. If I miss one, feel free to do it yourself.)