Look at the stars from different places on earth... you see totally different sets of them. That only makes sense if we're on a ball. Sailors have used that for navigation forever, long before NASA. The horizon thing is solid too, you can watch a boat go over it with your own eyes. His points sound logical until you check them yourself, which is what he says to do. The curve from a plane window is subtle, but there are videos from high-altitude balloons that show it clearly. It's easy to get stuck on the questions if you don't look at all the answers that are out there.