Manipulating and perverting what god created is not holy if this was the case the darkside in the starwars is holy which we know it isn't.
That would mean we wouldn't be allowed to create
anything, you idiot. Alchemy is a term used to refer to early scientific study. There's nothing unholy about that. Also, the darkside from Star Wars isn't actually real, or subject to the rules of the Castlevania universe; it's therefore absolutely irrelevant.
um, no they aren't. Alchemy screws with the natural "godly" order of things. If god made one thing gold the church looks at it as not our place to change it into something else.
They've never looked at things that way, any more than they've considered it heresy to turn a bunch of rocks into a church. The real-life concerns the church had with alchemy where that it involved sorcery or witchcraft, not that it involved changing God's creation: mankind does that every day, as does everything else.
The Church was trying to fight the crusades
Actually, it wasn't. Historically, the crusades hadn't started when LoI is set.
You think the government is gonna listen to me if I'm captain of a battalion of troops and give me permission to go on a crusade to invade a caslte and kill a vampire, no they're gonna look at me like I'm nuts unless I give them proof to take hundreds of men into what could be a pointless battle.
Given the description LoI gives, it seems the church is fully aware that there
are monsters in the castle, but doesn't want to fight them. Which is ludicrous: the church isn't going to screw around killing heathens in the Holy Land if it's got perfectly servicable demons right in it's own backyard.