What can YOU say in six sentences?
1) Forget this 'ships disappearing over the horizon' thing, nobody claims it is a perfect flat plane, nature likes curves so think of it as an inverted saucer with the North Pole at the top.
2) Note that people who insist there is a southern hemisphere have filled it with endless empty seas or barren continents so as to avoid explaining what is there ... well ... that's a bit convenient .. !!
3) Those that insist there's a southern polar area tell stories about it with characters like Amundsen, Scott and Shackleton, have you ever read these stories, talk about far-fetched boy's own stuff, you would read more likely truths in a comic book.
4) They say communications satellites wouldn't work with a flat Earth, when did you last see a satellite dish pointing downwards ?
5) I've met several Australians who claim to be from 'down under', well ... they were all standing the right way up when I saw them.
6) ... And most important of all, those who believe in a round Earth are clearly heretics, and should be thrown over the 'edge', if the 'edge' isn't nearby, I'm sure we can find a convenient cliff.