No, I don't want to reopen the whole thread. What I do want to do is present an idea, and see what you think of it.
A vampire is repelled by a cross. A cross is the symbol of the Christian faith. Hence a symbol of any faith will effect the vampires. (so the logic goes).
Well, what if the second statement is irrelevant?
Why is the cross a symbol of the Christian faith? Because Jesus was crucified, and died on a cross. Why was it a cross? Because that's what the romans used.
Suppose then that the Romans knew about vampires, and that the cross repelled them. Using a cross to kill people (slowly) on would therefore keep vampires away from their "entertainment".
This means that the adoption of the cross by the Christian faith would be merely coincidental.
So why are they afraid of the cross?
Maybe they aren't. Maybe it's the Ankh - a symbol very close to the cross. The Ankh is a symbol of life, it is anathema to a vampires. Suppose that is what affects them. The ankh, representing life, will kill the vampire. It may be slowly, requiring a great deal of force to emplace it into the dead flesh, but it would work.
As I stated above, the cross is similar to the ankh. What if all vampires know that something like the shape of the ankh can kill them. Maybe that is the only way to destroy a vamp intelligence, to attack it with an ankh (probably a certain magical artifact). All vamps know this, but fuzzily, so are terrified of the ankh, and anything that looks like it.
The cross looks sufficiently like one to a vampire.
However, most vampires would not know the difference, so are terrified of crosses too.
Vampires will not know the difference, except ones that have made a detailed study of life magic, death magic and vampires. ie they would have to have biomancy, necromanacy and vampiric knowledge. Not likely, but....
So, a vampire would not be afraid of a cross, only an ankh, and anything that looked similar to an ankh (this includes a cross).
The difference - a cross will only harm a vampire psycosomatically - so if a vampire knew it was an ankh that affected them, not a cross, he would not be afraid of the cross. Unfortunately there aren't many (ie one or two) that do know, and they all prefer to keep it a secret, 'cause the cross can't kill them...the ankh can.
There you are...and explanation of the vampires fear of crosses, but not any other religious symbol, and not requiring any particular faith of the user.
Comments?