Some folks' flat theories are rooted in Christianity (not sure where you got 'Christianism' from). Some are not, and are based upon understanding of a book or interpretation of a few experiments.
Sorry if i didn't cover the spectrum
Regardless, being linked to people that are christians would not make a theory that is necessarily christian. Natural selection and the origin of the species both have roots in christianity (monks and Darwin) but can conflict with most religious dogma.
A lot of historical scientists were very much religious (it was cool back then), a religious link doesn't make a theory religious.
What would make a theory religious to me would be basing it on scripture and attacking anything that is contrary to it's ultimate truth.
Flat theory has this forum, so would fail my imaginary test on at least the second count.
I think the point is that it's clear that Rowbotham, as evidenced by Chapter 15 in ENAG, purports that his theory is in support of and based on scriptural doctrine. Lady Blount and Voliva as well. Steadfastly so.
Whether the christian foundation upon which these founders of modern day flat earth theory still runs through FET today is debatable. The point of fact is that these founders were firmly rooting their theory in support of religious dogma.
Rowbotham mentions both Christian and Jewish religions as supporting Flat Earth, and has several quotes such as "In the religious and mythological poems of all ages and nations the fact of the sun's motion is recognized and declared."
Are these words of a Christian biblical literalist?
No. It shows that your conclusions of bias to be based on ignorance, and your research to be sub-par.
In ENAG, Rowbotham lays out his flat earth theory, findings, experiments, conjecture and otherwise. However, he cleverly leaves the best for last. Chapter 15.
Chapter 15 traces back to 'scripture' as everything he purports in the first 14 chapters with dozens and dozens of scriptural references that either back his claims or he backs into them.
According to Rowbotham, "That everything which the Scriptures teach respecting the material world is literally true will readily be seen.” According to his bible interpretation, the scriptures are the hypothesis, the initial theory, that the world is flat. As he continually cites biblical quotes, dozens of them, to prove such.
Lady Blount and her cronies do no better with their society in this regard. From The Universal Zetetic Society founded in 1892:
OUR MOTTO
For God and His truth, as found in Nature and taught in His Word.OUR OBJECT
The propagation of knowledge relating to Natural Cosmogony
in confirmation of the Holy Scriptures, based upon practical investigation.
RULES
1. Everything extraneous to “Our Object” to be avoided.
2. The so-called “sciences,” and especially Modern Astronomy, to be dealt with from practical data in connection with the Divine system of Cosmogony
revealed by the Creator.