Fares and (economic) equity

Transit districts, where transit is spread equitably (a stop every two blocks, a frequent network grid, excellent coverage) can be funded by a local property or sales tax--the beneficiaries of the service are also those who fund the service. But if you have people using transit who are from outside that district, who aren't paying the local property/sales tax to fund that service, they are functionally free-riding*, and in equity should be charged higher fares than those within the zone. In the reverse, using sales tax to pay for transit only works if that transit is equitably spread through out the sales tax area. Else people are paying for services they aren't using.

There is argument to be made that in either case, the affected folks do benefit, indirectly, through reduced  traffic congestion. But the match or mismatch of the taxed service area and the services provided matters. Fail to provide service while charging taxes and you'll get a tax revolt that revokes funding for transit. But spend too much money providing transit service to marginal transit-hostile areas, you'll go broke. Analyzing the cost per rider of any transit system clearly shows a wide variance in cost per rider by route (and even by route segment). So you have to hope that the transit planners have made a good 'bargain' in expending scarce and limited dollars to buy political support by providing transit service to marginal corridors/stations. (This hope is often in vain). 

In an equity sense (ignore the benefits of congestion mitigation), people should pay for what they get. But doing can be complicated, as it requires accounting for the cost of service and also the cost of infrastructure. In an ideal case, fares at an underground station with trains every four minutes should be much higher than fares at a ground-level station with one train an hour. However, because that underground station is located downtown, so the cost per rider of providing that service may actually be much much lower than at the peripheral surface level station with poor frequency. 

* A certain level of free-riding is of course tolerable, on the basis of generosity, charity, equity, and the cost of attempting to collect all revenue due exceeding the value of the revenue collected.