Here's something fun to do:
Browse the Flat Earth Society Forums and try to figure out which posters are actually serious. In my opinion, some of them must be serious, or else no one would have the energy to maintain that website. On the other hand, I can't believe that they can all believe that the earth is flat. I mean, some of those statements just defy too much reason for someone to actually believe in it. Then again, you just may be surprised.
By the way- I said to browse. Don't bother posting. If you think you have a chance at beating some of these people in a debate, you are quite mistaken. This isn't to say that they have good arguments or really a semblance of coherent thought. There are two specific reasons why you can't beat them in a debate, and here they are:
1. They don't listen to reason. Seriously. How else can you interpret their explanation for those NASA pictures that clearly show an Earth that is circular from all sides? Their answer- a conspiracy. Not only are the governments and scientific communities from all space-able nations involved, but so are satellite TV and GPS companies as well (they actually transmit signals via blimps and radio towers, since satellites are impossible). Those pictures taken from outer space are computer generated- 'cause everyone knows they had photoshop back in the '60s.
Some even claim that there are guards stationed along the ice sheet at the edge of the world to make sure people don't try to go over the edge. Somewhere along the way, you've got to realize that there's something not quite right in the brain with these people here.
2. They can always make up new rules to explain the discrepancies you point out.
Example- why can't you see over the horizon? Answer: Because light follows a curved path while on Earth.
Why does the sun set? Answer: Because the sun (and moon, which gives off its own light) are like spotlights- not isotropic light sources. They only shine on certain parts of the world at a time as they follow circular paths exactly 3000 miles above the surface of the Earth.
How do you explain the phases of the moon? Answer: There is another heavenly body, unknown to mainstream science, which is completely black and at times likes to obscure our view of the moon.
How do you explain gravity on Earth? Answer: There is no gravity on Earth. Instead, a "Dark Energy" continuously accelerates the Earth upward at 9.8 m/s^2. By the way, they do cede that other bodies in space have gravity, thus explaining the existence of tides (but not the fact that there are two tides a day!). As for why other bodies have gravity but not the Earth? Because the Earth is SPECIAL!
Why do distances in the southern hemisphere seem closer than what is suggested by Flat Earth geography? Answer: Remember how the GPS companies are involved in the conspiracy? GPS software intentionally sends planes in paths that make distances in the northern hemisphere seem longer than they really are.
If you come up with something else that's not right with Flat Earth theory, they'll just come up with some other new assumption that would explain the observation. If they can't come up with an explanation, they'll just give the "your a sheep who's been brainwashed by the mainstream scientific conspiracy COME ON PEOPLE WHY DON'T YOU OPEN YOUR EYES!!!" argument.
These two pieces of idiot behavior are a constant among all crackpot pseudo-scientific theories, including null science, autodynamics, intelligent design, and countless others.
I've also observed it among most ardent followers of every religious and political area of thought. Just an observation...
I said most, so don't anyone get mad at me.