Why are some Christians so simple minded?

I know not all are, but I see many Christians calling things a sin or satanic just because they look ugly and holy just because it looks graceful. Some can't even analyze the thing and just stick a satanic sticker just because it doesn't conform to their way of thinking. For example, when someone likes snakes, they call them evil just because of the bible symbolism (which is just purely symbolism). To repeat, I know most Christians aren't like this, but why are some of them like this?