I think the whole "movement" has been created from the fact that, scientifically speaking, earth is not round. At least not perfectly round like you see photos, because that's obviously water being pulled by gravity making it look like a soap bubble perfectly rounded.
First time I saw real photo of Earth I was somewhat shocked.
"real photo" - followed by a visualization that over-exaggerates the anomalies way more than thousandfold? (i.e. in the image earth is ~240 px high, given a polar diameter of ~12 000km we end up at ~50km per pixel. So even the difference between polar and equatorial diameter would be barely visible, and ~100m anomalies are 0.002px)
I'm not a flat-earther, but I'll daresay you couldn't prove that everyone who claims to have proof of a round earth is lying or deceived.
It's like some (alleged) variations of the young-earth creationist theory which posits that all the fossil evidence was deliberately planted by Satan to trick the gullible and only the true-believers can see though it. That's a pretty hard one to disprove.
First time I saw real photo of Earth I was somewhat shocked.
https://c.tenor.com/f7Pz19uaXFwAAAAC/earth-rotating.gif