I've yet to see any evidence at all for a flat earth. It's not a theory either. I would call it a hypothesis conspiracy, but personally, I think it's flat out insanity.
Tell me, what exactly is to be gained by NASA, the ESA, the CSA, and all of the other space agencies for lying to the general public about the shape of the planet we live on? Look in the sky. Literally, everything with the mass of a moon, planet, or star take on a spherical shape due to gravity. Does a giant, flat disk floating in a universe filled with spherical objects make any sense to you at all? It doesn't to me.
I find it hard to believe a person can sail or fly AROUND the earth if it's a disk. Also, explain to me the time zone and seasons on this flat earth of yours.
Your ideas are those from the Stone Age. Even some of those residents believed the earth to be spherical. 500 BC called... they want their ideas back!