I only have a few arguments about motorized bike laws US wide, and I know this is the basis of a popular one.
A moped STILL IS a registerable/insurable vehicle, despite that it is UNNECESSARY to get registered - as it has a VIN.
A motorized bicycle IS STILL a bicycle, despite having a motor.
There are 3 kinds of motor bikes listed in near every state.
Motorcycle (duh, we all know what a motorcycle is and it has a VIN)
Moped (it's a motorcycle with pedals, displacement over 50cc classifies it as a motorcycle and it has a VIN)
Motorbike (this is a dirtbike registered for offroad use only, though despite that, it has [guess what] A VIN.
They are two distinct things, and the nail has been hit on the head already - if there isn't a law REGULATING it or CONDONING it, then it is as we say, "LEGAL".