Most superstitions are relatively harmless other than the anxiety they can cause in those who believe in them. But there have been times they caused trouble.
The belief that cats were somehow evil and witch familiars caused people during the ‘Plague’ to kill cats, even burning them because they were seen as causing the disease. Ironically, since the disease was spread by fleas on rats, and cats kill rats… Killing the cats caused a boom in rat population which worsened the plague.
I’d call that a disadvantage.
-not my paragraph, full credit to person who wrote it!)