Earlier quoted context omitted.
Depends on the superstition, if it were "you should say 'black door' every time you see one [and you'll have good luck]" then it would make no difference. It would neither inhibit nor encourage those of the out-group. Let's look at religion: if my religion says "give money to orphans" then you don't need to fight it, it doesn't harm you, if it says "make everyone who's not part of our group subservient or dead" then…
"give money to orphans" is harmful to you when the target is your 90 year old mother for her social security check that would otherwise allow her to be financially independant. Doubly harmful when a very small percent, if any, actually goes to helping orphans and instead supports the continuation of the predetory practice.
If it were "force others to give money to orphans" or "steal money that's set aside for orphans" then you'd perhaps have a point.
Unless, you're trying to say it's impossible to have someone hold a [superstitious] belief that doesn't impact others negatively?