A random thought:

If you donate less than 10% of your income to a cause you believe in, or you spend less than one hour per week learning how to be more effective at helping a cause you believe in, or you spend less than half an hour per week socializing with other people who support the cause... then you are less instrumentally rational than the average christian.

edit: shokwave points out that the above claim is missing a critical inferential step: "if one of your goals is to be charitable"

edit: Nick_Tarleton points out that the average christian only donates 2.9% of their income to the church. And they don't go to church every sunday either. Also, being charitable ≠ doing good.

explanation:

The average christian donates about 10% of their income to the church. This is known as "tithing". The average christian spends about 1 hour per week listening to a pastor talk about how to become a better christian, and be more effective at helping the cause of christianity. This is known as "going to church", or "listening to a sermon". And going to church usually involves socializing with the other members of the church, for an amount of time that I'm estimating at half an hour.

And that's not counting the time they spend reading advice from other supporters of the cause (i.e. reading the bible), or meditating on how to improve their own lives, or the lives of others, or other ways to support the cause, or hacking their mind to feel happy and motivated despite the problems they're having in life (i.e. praying), or the other ways that they socialize with, and try to help, or get help from other people who support the cause (i.e. being friends with other christians).

The point I'm trying to make is that the christians are investing a lot of resources into their vaguely defined mission, and it would be sad if people who care about other, actually worthwhile causes are less instrumentally rational than the christians.

edit: oops, there's already a good LW article on this topic.