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In any case, there is potential for great good and great horror depending on how the magic in EGS is used. Used benevolently, it could usher in a golden age. Used malevolently, it could have the potential to literally destroy the world. Note the "literally" there. I'm not talking Fallout games "life goes on" sort of end of the world here (although I really like Fallout 3).
In short, the consequences of it being common knowledge are unknown, which is in part due to the limits of magic being unknown. Odds are some dude with magic can't blow up the planet, but who knows for sure?
With all that said, here is how I originally presented the question (in the interest of full disclosure, I said nothing about "destruction of the world" potential prior to compiling the results):
You can prove magic is real. Public knowledge would irreversibly change the world, possibly making it worse. Do you keep magic a secret? http://www.egscomics.com/?date=2010-12-06