To elaborate, items are generally banned because they have a destructive effect on server performance, bypass the claims system, are hopelessly buggy, are so balance-breaking that they make everything else pointless, or some combination of the above. It's not to prevent people from having fun or otherwise doing what they want.
Nobody wants a server that is a copy of another server if the only differences are that it crashes every five minutes and anyone can have their stuff griefed at any given time.