I have personally photographed the curvature of the Earth, with my own camera. As if there wasn't enough evidence already that thinking Earth is flat is ridiculous, you can literally go out and take a picture yourself.
I flew my quadcopter straight up about 1000 feet above the ocean (nearby mountains kept the height limit legal) and took a picture of the horizon. You can go into ANY image editing software, pin a line at the edges of the horizon, and what do you know, there's a small bulge in the center. From the curvature of Earth. With a high enough resolution camera you wouldn't even have to fly, you just need the ocean to ensure a level horizon. No weather balloons, no rockets, just literally a camera and either a mountain next to the coast or a RC helicopter.
On top of the fact that a flat Earth would imply the nonexistance of gravity, which means that satellites aren't real, which means that GPS isn't real even though it clearly works. This is absurd. Go out and take a picture yourself if you're so keen on pretending that millions of people kept a ridiculous secret for thousands of years.