Bloodletting? That's just too crazy for words. The OpenBSD people produce first class code that's solves real problems in real production, and you compare it to witchcraft?
If you absolutely need speak in parables, do it with something that represents an earlier common practice, for example with producing houses with hammers and nails instead of modern pre-fab concrete blocks. But even that is stretching it a bit too far, the productivity difference simply isn't comparable.
Bloodletting isn't witchcraft. It removes iron from the body such that virii and bacteria trying to reproduce would have problems. It makes the host environment more hostile to the invading species. It has a lot of negative side effects and wasn't very effective, but it did have an effect.
Of course, some people did bloodlet for reasons that didn't help, but without knowledge of bacteria, many were just trying their best with what limited knowledge they did have.
If you absolutely need speak in parables, do it with something that represents an earlier common practice, for example with producing houses with hammers and nails instead of modern pre-fab concrete blocks. But even that is stretching it a bit too far, the productivity difference simply isn't comparable.