[VLM]

"perfectly within its rights to impose a licensing requirement"

How so?

I can think of two example of near unanimous modern agreement where lower governmental levels are not allowed to impose additional randomly purchased rules on subjects regulated at a higher level, its a thought crime to even suggest the rationale behind these historical issues:

1) Poll taxes and election tests

2) Enforcement of immigration law

[pdabbadabba]

Well of course there are certain licensing requirements that a municipality cannot impose. But you remain very far from showing that a license to operate a taxi -- an area that is subject to strict regulation in virtually every municipality in the U.S. -- is one of them.