I just thought about this and I just can't figure out why private servers are regarded as illegal. Or IF they are actually "illegal."

What I mean by that second part is, is "illegal" the correct term to be used, or is it meant in a way of "unsupported" or "not endorsed by SEGA," not so much a literal, in-the-court-of-law type of illegal?

For that matter, illegal by which countries laws?