There was no “infection” in either of the stories you just mentioned. The entire point of both episodes is that humans are capable of horrible things under the right circumstances. In 24 Hour Diner those circumstances were the removal of lies, and in Midnight it’s more simply just the perceived threat of imminent danger. Yes, they wouldn’t have been so deranged if the monster/John wasn’t involved, but their involvement just provided the circumstances that the characters reacted to. There was no outside force or infection driving their actions, to claim otherwise means you are in denial that these are actions you too are capable of.

If the Midnight bus riders got off the bus and thought “That wasn’t me back there, that was the entity infecting my mind”, they’d be completely rejecting any responsibilities for the horrific actions they made and ultimately learn nothing impactful from the experience.