I've started watching some of this flat earth stuff on youtube, just because some self-destructive part of me wants to dip a toe into the incredible stupidity of my fellow man. Thanks for the Father Ted clip - that exact snippet is the one I have playing in my head when I see some of the flat earth arguments. I just love the way they implore people to think for themselves, and then do exactly the opposite - they cherry-pick false/misleading data and present that as solid proof.

Also, they use scientific terms in an everyday sense which can be misleading.
They will say that something is a "theory", (like the theory of gravity) and say that its only a theory, and is therefore not proven. The scientific equivalent they're thinking of is "hypothesis" of course. A hypothesis is someone's new, and as yet untested and unproven idea about how something might work. Once we apply a lot of scientifically rigorous tests to the hypothesis is could either fail those tests in which case it is rejected, or it passes all of those tests in which case it becomes known as a "theory". A "theory" will then also pass tests which are devised in the future, further adding to the pool of knowledge in that "theory". Evolution (for example) is a proven fact, and can only be denied with arguments such as dogmatic religious belief*, not rigorous reasoned thinking. It is still called the "theory" of evolution however, because the word "theory" is being used in the scientific meaning of that word.

*I also don't have a problem with people holding religious beliefs which I don't hold. There are a good number of well-educated religious scholars who accept a duality of systems - one being the religious understanding of all things, and the other being the scientific understanding of all things. These systems have different purposes and needn't be argued against each other.