Debating flat earthers is fairly similar to banging your head against a wall. The logic that the government lies about everything, therefore the earth must be flat is extremely faulty and ridiculous.

People in the 17th century didn't believe the earth was flat. The earth has been treated as round by the educated since the 5th century BC. It is fun to paint the medieval period as backward, but there isn't much truth in it. It is like the myth that Columbus was trying to prove the earth was round. But everyone already knew that in his day. What he was trying to prove was that the earth was small enough to sail west to India. He had trouble getting a ship, because people who could math knew that it was a longer route.

I generally think that human history is much longer and more complicated than we think. as you say, I expect there have been people that have known that the earth is round for several thousand years but the point that I'm making is that people were still having this discussion, just like this, in the 17th century

like most things, it's usually an exercise in developing a coherent argument yourself and perhaps edifying for somebody who reads it