Transportalization.? Very plainly real. Aliens.? Believable. Magic.? Fine. Vampires however.? Foley. Trite. I will never so much as consider such a tropey thing existing. Vampire-Aliens are different of course.
I'm sorry I've been attacked by enough varieties to know that they're a thing.
You have been attacked by lepers and rabid men with albinism. I refuse to believe something so caked in theistic ideology and concepts holds any water.
It's just silly to draw a line in the sand here of all places. We got satyrs nymphs trolls and I've seen at least one harpy on here, what makes a human vampire any less feasible.
I have already told you why. The origin and mythos surrounding the classical vampire. If I held a crucifix up to a vampire and it genuinely shrieked in agony it would almost entirely shatter my worldview.
Most of them don't, I've tried that. I don't make a habit of like. Encountering them but the LA I frequented certainly had a few dens. I take more damage walking into a church than a vampire would.