Flat earth nonsense is not worthy of any response other than ridicule.
ridicule is not evidence and should not be taken seriously by any thinking person.
I say, debate ideas on their merit. For years we were told that Russia was our enemy by the MSM. Then we learn Russia helped expose Hillary Rotten Clinton and defeated ISIS in Syria. Yet if you say so you are still ridiculed by some people.
I have learned a wise person look at the merit of ideas and remain critical of self-proclaimed "experts" full of ridicule and bombast.