Comment by potato3732842

>This money was already taxed when the individual who pays the babysitter received it. It's questionable whether the society as a whole benefits from taxing babysitters.

Replace babysitter with any government regulated and licensed profession and the motives become clearer. The government gets power by forcing things above the table because once above the table you can be forced to transact with who they want and how they want and those parties then become dependent upon government to a degree.

There's no such thing as cash under the table land surveying, for example.