There is plenty of evidence that the earth is round.  There is also plenty of evidence that NASA is to be trusted.  So why should anyone discard that evidence in favor of believing that the earth is flat?  What is your best, most incontrovertible evidence that the earth is flat and NASA is lying?  Remember to cite your sources.

Hi, friend.
I think of it in this way. A computer programmed to do a certain function would perform it with whatever data we feed in. Even if the data is wrong, the machine would process and give a logical answer (according to what we fed in). What if we were wrong in our assumptions? We were taught from childhood that earth is round. Don't you think we have already accepted that without questioning?
Could you please mention a few evidences you speak of? Which doesn't have any assumptions behind them and would appease a straight forward logic? The FES apparently doesn't approve of photographic evidence (Thanks to photoshop and similar software). I'm not yet convinced of both theories, to be honest.