Such concepts are rarely completely "self-generated", but mainly consequences of misunderstandings, often paired with ideological predispositions. As in the case of Mudcat's favourite "mondegreens", few such errors seem too weird not to be shared by many others.

I am no longer following the "Darwin's Witnesses" thread, but I know exactly what you are talking about in that context. Science, religion, history, and politics capture the imaginations of imaginative people.

Quite a number of books have been written about common misconceptions - common but often caused independently by a large number of inventors, including serious journalists and scientists.

Of course, most authors of those books appear as patronizing and sneering; I do not want such a reputation if there is no acute necessity. Still, whoever joins a discussion has the responsibility to correct the other participants' relevant misunderstandings, often very basic ones. Tedious and dangerous.