Q: Is smearing lamb’s blood over my doorway unnecessary?
A: Yes. You make sacrifices because they’ve always worked for your ancestors. However, your ancestors were not well schooled in statistics and experiment design. They offered sacrifices only when times were dark and all other means had been exhausted. Since (for example) the amount of rainfall is random, regression to the mean suggests that it will tend to get better after it has done really badly. Therefore, most sacrifices seem to work, and you are violating zoning laws and pissing off your neighbors for no reason.
(Inspired by Karen Armstrong’s Buddha.)