People come up with ideas that are clearly and manifestly wrong when they're confused about the reality. In some cases, this is just personal ignorance, and if you ask the right people they will be able to give you a solid, complete explanation that isn't confused at all (evolution being a highly available example.)

On the other hand, they may be confused because nobody's map reflects that part of the territory clearly enough to set them straight, so their confusion points out a place where we have more to learn.