Is it NOT rational self-interest to "invest" your personal time and resources in things that increase your marginal utility from that investment? Yes, it is. That's classical austrian economics.
You might like to invest X% of your time in entertaining yourself, if your marginal UTILITY from the investment is positive. Another person might PREFER to invest x% in feeding the homeless as a result of a religious motivation.
PROVIDED IT RAISES THEIR MARGINAL UTILITY, then it is perfectly rational. If you do not believe that premise, then you do not believe in laissez faire, free market economics, given that it is one of the necessary basic tenets.
As far as your completely separate subject about the "harm" religion has done, nice collectivization. If you for example, were a Catholic, did you burn witches? Nope. So, explain how you are liable for errant witch burning 400 years ago, then. You personally.
What hypocracy from you - extolling the virtues of the individual then turning immediately around and collectivizing people.