To be quite honest, it's not that it's wrong, it's that there really isn't much of a point to it.
You don't need to really keep tossing down the same thing repeatedly. "Haha remember that one thing I made? alright here let me buildbot it again." And if you're not really the kind of creative person who can make unique things, then building servers aren't really for you anyway.
I don't agree with it being bannable though. Fortwars are typically loaded as it is and they normally have a rule against killing builders so having a 'faster start' isn't an issue. If anything, it's bringing more action into the server faster. And you still have to wrench/print/event everything.
Though not directly related to buildbot, but still on similar terms. @BT and img2brick are far worse to be using. They don't provide any purpose but spam. A message could be made in print bricks, or an event. An image could be posted as a link in chat, or as a link in an event.