I have many times been offered the opportunity to debate on the topic of whether or not the Earth is flat. And I have declined. I've been accused of being afraid to engage in such a debate, but really the reasons have nothing to do with how I might fare, and everything to do with the nature of the debate itself.
There Is No Debate
The shape of the Earth is not a matter of opinion, it's a matter of fact. The Earth's curvature can be directly measured, and has been by geodetic surveyors over the last 200 years or so. Photographs of the Earth have been taken from space, and however much the flat-Earthers cry "fake," they have never been able to prove the claim, and never will be able to, because the photos are genuine.
The flat-Earth model, such as it is, can easily be disproved by something as simple as a sunset, no matter how many torturous hoops flat-Earthers jump through, and no matter how much they have to make up out of whole cloth in trying to prove otherwise.
In short, it would be like having a debate on the topic of triangles: "A triangle has three sides. Pro or con; give reasons for your position." There's just nowhere to go.
Agreeing to debate on a topic on which there is no valid controversy gives the topic an aura of respect that it does not deserve. It elevates the purveyors of those ideas to a status they have not earned, relieving them of the burden of intellectual rigor of any kind, and encouraging anyone with a silly hypothesis to pass themselves off as an original thinker, or worse, a "true scientist."
The notion that all ideas have equal validity is something pseudoscientists use to play to people's sense of fairness and to gain a tactical upper hand by proposing that their "evidence," not matter how spurious, be given the same weight as scientific fact. But accusations, assertions, and outright lies are not facts and should never be treated as such. Ridiculous ideas deserve to be ridiculed, not debated.
Flat-Earthers Don't Do Debates
A debate is a formal argument on a single topic. But go to YouTube, search for any flat-Earth "debate," and you'll find that there is nothing formal about it, nor are any of these (often excruciatingly lengthy) "debates" held to a single topic, not even one as broad as "is the Earth flat?" They are nothing but a free-for-all, with plenty of personal insult and off-topic rambling, and whenever a flat-Earther gets backed into a corner on one aspect of their "evidence," instead of defending the indefensible, the flat-Earther will change to a completely new tack, hoping that the shifting of gears will throw everyone off the scent.
And for these reasons, whenever someone asks me to debate Jeranism or Jeffrey Grupp or DITRH, I just say no, knowing that nothing will be gained, either by me or by the quest for the truth, from such an exercise.
And I suggest that anyone else avoid this useless path as well.