One thing I’ve learned over the course of my life is that if someone believes something strongly enough, the chances of convincing them otherwise is pretty close to nil.
I suppose showing the flat earthers photos of our planet taken from space, photos of other planets, looking at the moon outside their own front doors would be met with protestations that everything was faked by “them”. Taking them up in a plane high enough to see the curve of the earth (like in a flight between continents) would be met with “It’s all an optical illusion”.
I’ve just used one example of bizarre beliefs. There are many others — many that would be very contentious to state. That’s not my aim. This is not a matter of “I’m right and your wrong.”
Whether you believe somebody else’s beliefs are absolutely screwy, you should in the end respect their beliefs. It’s what they believe in their hearts. To them it is The Truth.
In writing convincing fiction, this is a very important concept to embrace and understand. Terrorists believe so wholeheartedly in something to be willing to do horrible things and lay down their lives doing them. That’s very heavy duty, to believe something that strongly. As an author, it is our job to make this understandable to our readers.
Once a writer understands the belief concept, convincing characters with strong beliefs will become more believable. How many times have we all, as readers, put down a book because something a character did was just too unbelievable. The fault lies with the author who didn’t — or couldn’t — understand and hence wasn’t able to convey the character’s very strong belief in the character’s actions that was needed for the plot to work. Groundwork should have been laid beforehand and it wasn’t because the author was unable to perceive this fault in his/her writing.
So don’t try to change flat earthers minds, try to understand them. Your readers will thank you.