They didn't die and mystically come back as nocturnal ubermensch to some cursed half-life, despised by God and shunned by the decent. The whole idea is ludicrous. The vampire is not physically superior to your everyday human. There are some subtle and less than subtle differences, but overall, there is no reason to spend your time and energy trying to find a way to become one. God does not hate vampires.
Crosses are just religious symbols and occasionally nice accessories.
No self-respecting vampire is going to run screaming spitting or hissing from a cross. Holy water will not burn or even cause discomfort when touched or ingested. Oddly enough, garlic is usually well liked by vampires. I have never found a single vampire who wasn't partial to a well grilled bit of garlic toast. Vampires are not exempt from natural laws.