The OP asks for fruits and by their contributions, flat-earthers only prove they are bad fruits.
.
The bad fruits of flat-earthism.
.
Flat earth severs the bond of heliocentric lies that enslave the world. Flat earth exposes the malicious kingpins who steal billions of dollars to indoctrinate the masses. FE destroys scientism, Big Bangism, evolution, global warming, alien invasion, dwindling resources, pole shift, life on other planets and destroys the need for spending billions of dollars on projects that enrich the few who intend to enslave man. Anne Catherine Emmerich says the false sciences taught by demons to Enoch's grandson Hom about the universe and creation, are the 'mothers of all heresies'. Pg 48 Life of Jesus Christ book 1.
When a special key like FE has been provided in order to throw off the chains by which man is enslaved, the good that comes from it is 100% good fruit, 100% of the time. Only the person who desires to remain enslaved within the pagan lie would even suggest that freedom is bad. Unless of course, he himself is one of them.