If that's your argument — that you are only required to be licensed to drive only when driving vehicles that are required to be registered — that fails because personal autos are required to be registered:
(1) As a condition precedent to the operation of any motor vehicle upon the streets or highways of this state, the motor vehicle shall be registered as provided in this chapter.
(2) The registration and the fees provided for registration shall constitute a privilege tax upon the operation of motor vehicles.
Tenn. Code § 55-4-101(a). As to the definition of motor vehicle, the § 55-1-103(c) and (e) states:
(c) “Motor vehicle” means every vehicle that is self-propelled, excluding electric scooters, motorized bicycles, and every vehicle that is propelled by electric power obtained from overhead trolley wires. “Motor vehicle” means any low speed vehicle or medium speed vehicle as defined in this chapter. “Motor vehicle” means any mobile home or house trailer as defined in § 55-1-105.
(e) “Vehicle” and “freight motor vehicle” means every device in, upon, or by which any person or property is or may be transported or drawn upon a highway, excepting devices moved by human power or used exclusively upon stationary rails or tracks.
So let's put that all together. A personal auto is a vehicle because it is a device in which a person or property may be transported or drawn upon a highway. Neither the term transported nor drawn is limited to commercial vehicles, contrary to your assertion. That's the flaw in your argument. And since a personal auto is a vehicle and is self propelled, it is a motor vehicle under the code. Thus since it is a motor vehicle, it is required to be registered. That is pretty much what the court will tell you in response to your argument.