Why did Aleister create the Science Side?
As of revelations from New Testament 19, yes we now know.


   Aleister's first daughter died after caching Typhoid fever. It wasn't anyone's fault, it was just a stroke of ill fortune. So, Aleister decided to destroy all misfortune - that is, destroy all magic and religion. That would remove all forms of coincidence from the world, and no one would ever be unfortunate again. (Though, as Touma points out, that would mean that no one would ever be lucky again either.)