[abduhl]

This source would disagree with you about the reason for taxi medallions:

https://books.google.com/books?id=VXpyNs5EaHEC&pg=PA119&lpg=...

It confirms the story that I have heard previously that taxi medallions were introduced to protect consumers. This doesn't mean that profit was not a reason but I'd like to see something that shows the "explicit" reason you state.

[kazinator]

I suspect it's not just for the consumers but for the image of the city. Cabs are one system that visitors interact with immediately, before nearly anything else. Grotty cabs make a bad impression.

[jon_richards]

So does a 2 hour taxi line.