Laws don't manage to prevent abuse on anything already lawed, I don't trust them to help here.
I actually do have problems with cyborgs, medical ones included, but that's outside the scope of this thread. Although if you insist on referencing them: Borgs can be detonated, they're slaved to the station AI, they're slower than sentient bots, they're significantly more complicated to repair, they're much more expensive to build, etc.
Server rules are not a catch all for behavior like validhunting. They make it possible to punish the action, but intent can be hard to prove, and admins don't see everything.
You'd be surprised, then.
Hacking MULEbots serves a legitimate function, and that shouldn't be exchanged just so we can have more sentient bots.