Is there a word for a person or group advocating a belief that has been disproven?

What can I use in this sentence:

People who hold on to a belief despite evidence that disproves the belief are called ______.

For example:

"Freddy and his friends were ______, they were advocates for the Flat Earth Society, preaching that the Earth is flat like a mat in the hope of new proselytes."

Like dogmatists but specifically about a prior belief since disproven. I could use zealots or fanatics, but again they do not seem to cover the exact meaning I'm after, i.e., the active advocation of a disproven idea. I came across the term non-evidentialist but would prefer something without the negative prefix (if possible), and it is probably too wide a term. The word fundamentalists tend to have religious connotations, though it may fit as some beliefs can be advocated in a similar manner to religious fervour (hence the use of proselytes above). I quite like the word sheeple? Though again, not the right context. I'm wondering if the word I am after does not exist.

Solution 1:

People who reject ideas in the face of widely accepted evidence can be called denialists. The term can be tailored to fit specific kinds of denialism depending on what commonly held views are being denied - examples include science denialists, Holocaust denialists, climate change denialists, or in your specific example, round-Earth denialists.

Your proposed term of sheeple doesn't really fit, as the term connotes people who mindlessly go along with commonly held beliefs without scrutinizing them. There is an aspect of being easily misled consistent with denialism, but there is also the connotation of belonging to a majority "flock". In fact, denialists may call other people sheeple for buying into commonly held beliefs. Denialism is often associated with "independent thinking" (regardless of how wrong or misguided those thoughts may be), which doesn't really fit with the mindless, accepting nature of sheeple. Sheeple generally accept the default worldview, but denialists actively reject it.

Solution 2:

They are delusionalists.

The adjective delusional is defined by Lexico :

delusional [adjective]

Characterized by or holding false beliefs or judgements about external reality that are held despite incontrovertible evidence to the contrary ....

And Merriam-Webster adds the corresponding noun

delusionist [noun]:

one given to deluding or to having delusions