I didn't say Ghosts were about precognition, I said just like Vamp, ghosts are in the acceptable side of the paranormal that fit in MGS, vampires aren't.
If you really see no difference and there's no reason to pick and choose, like I said, what about aliens? Literal voodoo zombies, wizards? etc etc
There were voodoo dolls in MGS 4, and MGS 2 left a premise that there were Aliens in control of the White House. I'm not saying that I would've liked for there to be actual Aliens. But, considering all of that, why do are you so intent on believing, that it would've been a stretch of the imagination to include actual Vampires?
MGS started out like a fantasy military series. This is regardless of the blanket answer of "nanomachines" for everything from MGS 4.