Here's a question: Do you flat earthers believe half the earth is lit up by the sun?
Take the spherical earth, split it open at the bottom and stretch the bottom out to a wide circle. This is how flat earthers imagine the earth to be. The equator is now a circle. This also means the southern hemisphere is now a lot bigger than the northern hemisphere. Unless you shift the equator line out a lot, but that would require a lot more shifting of countries etc...
Now, the sun travels more or less around the equator, like a "spotlight" (says the faq), how can it light up half the planet? Well, the light would have to be shaped like a D to cover the same area it would if the earth was a sphere. If you say "who says it has to?", then I say, "we, as a people, observe the sun like this. The human race observes the sun lighting up half the planet". This is undisputable.
Now how can a spotlight create a giant D shape? Why does it have a sharp cutoff point through the north pole? How does it light up southern countries X miles from the south pole, equally and opposite the way it does northern countries X miles from the north pole, when in the Flat Earth diagram the north and south poles are shaped completely different?
Get in a plane and travel south. Pass the south pole, and begin heading north again. No, you didn't miraculously turn around because the government brainwashed you. What you did was fly around the bottom of the spherical earth.