system
Given the following post, respond as if you're commenting on Reddit:
human
Do traditional vampires prove the existence of a Judeo-Christian god? How does this affect the world?

In films where there are vampires that get burned on contact specifically with crosses, be they wooden or silver or what-have-you, wouldn't the other religions in the world kind of look at this with a sinking in their hearts?  Note that I am discluding I Am Legend, wherein vampires are repelled by the signs of the faith they held while human out of existential horror.

Moreover, does the cross need to be blessed, or holy in some fashion?  I've seen several movies where the plucky protagonist fashions a makeshift cross out of two handy pieces of wood... so would "accidental" crosses work the same way?  Would walking through the woods, or a construction site, cause great distress to a vampire?
gpt
No, not necessarily.

This does depend on which type of vampire we're dealing with - there are some who deal with religious materials without any issue at all. Likewise it depends on which world we're talking about, as different worlds have magic that works in different ways.

For those who are repelled by crosses, there are some (A certain Mr. Dresden from Chicago, for example) who have found that it is the energy of faith that actually works against the undead. He has a good friend who is a devout Christian, and for that friend, the cross is a powerful tool to ward off the undead. The key here is that it's not the symbol that matters - it's the faith of the wielder. Mr. Dresden does not have faith in any god, but he has an enormous amount of faith in magic itself, and with that faith has managed to repel the undead (and werewolves) with symbols of magic.

A similar phenomenon to the one above can be observed in the Discworld - the more people believe in something, the more powerful it becomes. Gods have come into existence there simply because enough people believe in them.

tl;dr It's very possible that the cross is repelling or harming the vampires because of the faith that people have in it, not because there is something magical or special about the shape, or because of a certain God.