The real reason taxi drivers don"t want the home base tracking their travels is because they would have to give up their current practice of taking longer routes to destinations in order to rack up larger fares for the longer rides.
I also think the other objection to having a GPS device tracking thier every movement would be that it might disclose the pickup and dropoff points of drug and hooker deliveries; which are common forms of revenue for taxi drivers. A record of a driver's nightly stops could be capable of being used as a means for law enforcement to track these activitiess and use the information to set up sting operations and to use as evidence in court as is now done with phone records.
I have personally called out taxi drivers for taking unnecessarily long routes to my destination. When reporting this to thier dispatchers, I usually get an apology, a refund; and in one case, the driver was fired on the spot.
Personally, I think any honest driver would welcome GPS as a means of plotting the shortest path to a client's destination, thus saving the client time and money.
Dennis Miller Disclaimer: Of course, this is just my opinion; I could be wrong.