I think you're all confusing fans with purists. Fans tend to get excited about a project involving their favored franchises much more easily and even give it a better chance than the general public will (for example, look at Judgment; the general consensus here is pretty damn positive for it, everywhere else it's strongly in the negative).
Purists, however, are never satisfied unless a film adaptation is 100% faithful to the book, video game, comic book or whatever source of origin inspired the adaptation. These are the sad fanatics who blasted Fellowship of the Ring for not including Tom Bombadil prancing around festively and singing for fifteen minutes; the same pathetic bastards that rail against the Harry Potter films for every tedious piece of minutiae from the books that's (mercifully for the rest of us) left out; the same shreiking minority that already hates the Star Trek reboot because it might not be entirely faithful to the original series and films, which themselves slaughtered continuity without shame.
Being opposed to the Castlevania film as we've come to understand it isn't a sign of purism necessarily. Those involved with the project have shown little to no interest in the original stories and have a terrible track record in producing other films. Skepticism and cynicism regarding this film aren't quixotic or reactionary, they're pragmatic.
As I heard last, there isn't even plans to have the protagonist use a damn whip at all, let alone the storied Vampire Killer. That's like Ghostbusters without proton packs or King Arthur without Excalibur, it's not some summary detail of the story, it's part of the story and scheme itself. I don't care if they tweak timelines, omit certain characters or make up their own, or add a different take, within reason, on the central thematic elements of the story. But if this movie has full black leather one piece costumes, techno music, or firearms used as weapons as I suspect it probably will, count me way out.