By saying the excuses, you are listing what they are being brainwashed into believing,
That's still assuming someone is brainwashing them. Stories, myths and legends can all be spurned through very different channels.
since no logical person would think that way.
Faith, superstition and/or beliefs has nothing to do with logic. And don't even go there, keep in mind that religion (wether or not they're true) are just as much faith as superstition is. Logic has nothing to do with it. Opposing that makes an ass of whomever opposes it. Einstein, Mendel, Darwin, Aristoteles, etc etc, were all intelligentl people, far outdoing any of us posting on these forums in logic. And yet, they all had a faith. While not being superstition like we normally view it, it's still included in having faith in a truth or a system you can't prove.
Claiming that "logical" people would dismiss already widly accepted facts is to disregard how the human mind works. Just the "fact" that you can summon beasts with magic is enough for learned natives to claim that beasts of the night is spurned from mages. After all, if they're not spawned by magic - where did they come from? Where do undead come from?
I'm sorry, but your arguments is just plain flawed Ripkill. Logic does not denote knowledge, and logic per definition would not tell anyone in Ravenloft that the dangers of the night does NOT have something to do with the presence of magic. In fact, even an outlander caster could easily construct a theory saying that it is indeed the casters that cause the high amount of magically empowered and blood thirsty monsters.
You sit on OOC knowledge about Ravenloft, hence, you can spur theories. But to your character, it could in fact be some mage somewhere creating these creatures on purpose, with a defined goal. It's the same for Natives. They believe that when someone casts magic, they are gathering their powers from demonic sources.
An illiterate people, with no prior knowledge about magic, brought up on stories about the evilness of magic - could in no way come to the conclusion that magic is just a tool.
If I told you the holocaust was a good thing, and that the Nazis were right, you'd probobly disagree with me, and even dislike me. The same reaction is gathered by Natives when confronted with magic. It shouldn't exist, and those times it do exists, it's always bad and will always result in demon summoning in the end.
It's neither misinformation fed to them by some higher power, or a notion of stupidty. It's simple human nature, and simple reactions from an illeterate population beset by dangers every day of their lives.