The main problem with "illegal numbers" seems to be that for any illegal number a , which represents someone's intellectual property or trade secret A , I can easily create two original pieces of intellectual property B and C so that b + c = a .
Give us an actual example of b and c that are created without knowledge of a, and you may have case. But information theory says it is unlikely, if a is deeply original and not derivative of something like b and c to begin with.
Of course, here we come back to the "color" of bits; one is unlikely to be prosecuted for "copying" a song one has never heard. Though cases like My Sweet Lord are enough to give one pause.