I disagree that the space program is the main issue for the FET. It is used often as a rebuttal against FET, but for FE'rs, it is really not an issue. Quite simply, Flat Earthers tend to believe that a portion of the information we are told about the space program is falsified. And, we are not alone in these beliefs. Evidence is posted all over the internet from people who believe the same way. I will not bore you with links, as I am sure that you have already seen this for yourself.
Bendy light and the other stuff you mentioned are just theories that try to explain phenomena that people observe. The theories could be right, they could be wrong, or they could be somewhere in between. The point is that we do not just settle for the information that is spoon fed to us. We look at all ideas, alternative or mainstream, and try to decide for ourselves which ones seem to be the most correct. Some of the information you were taught in school may be correct, some of it may be wrong. Here, you get the opportunity to discuss and debate those ideas and come to your own conclusions. This is the reason that there is no single flat Earth theory. Everyone has their own ideas and we respect everyone's individuality.