Overcharging and refusing fares is what we get now in the regulated system. In practice, "gypsy cabs" often serve neighborhoods where the regulated cabs don't bother to go.
Regarding "rob riders", direct robbery is still illegal - you don't need industry-based regulation to accomplish that end. But if by "rob" you really mean "cheat", the market has evolved multiple mechanisms to make fares transparent. One of these is the "zone card", where the price of the trip depends on how many zones away your destination is from your source. Where jitney traffic is legal, the zone map and price list could even be printed in a sticker on the door so you can see the expected fare before you get in.
Regarding "clog the roads", a functioning jitney system makes it much less necessary for people to own personal cars. (and as a non-car-owning manhattanite, I'd love for the roads to be "clogged" with cabs if that meant I could reliably find one to go to Brooklyn or Queens). (And again, major roads like 42nd street "clogged" with cabs is something the current system produces in spades.)
Regarding "rob riders", direct robbery is still illegal - you don't need industry-based regulation to accomplish that end. But if by "rob" you really mean "cheat", the market has evolved multiple mechanisms to make fares transparent. One of these is the "zone card", where the price of the trip depends on how many zones away your destination is from your source. Where jitney traffic is legal, the zone map and price list could even be printed in a sticker on the door so you can see the expected fare before you get in.
Regarding "clog the roads", a functioning jitney system makes it much less necessary for people to own personal cars. (and as a non-car-owning manhattanite, I'd love for the roads to be "clogged" with cabs if that meant I could reliably find one to go to Brooklyn or Queens). (And again, major roads like 42nd street "clogged" with cabs is something the current system produces in spades.)