I ran a private server years ago. Two things people in this thread are getting wrong: The engineering is way harder than anyone gives credit for. You're reverse engineering a server protocol from the client binary, writing your own spell systems (thousands of spells, each with edge cases), pathing, instancing, combat mechanics. Then scaling it for a few thousand concurrent players on hardware you're paying for out of…
No, it's inevitable. There's nothing positive about using the law to crush competition.