THe small loss in fares is more than made up for by the increase in speed-of-commute (and ridership gains among the honest) and the better capital efficiency.
The 99%+ of honest riders is today made to suffer through barriers and stops that take too long, just to accomplish a task (ensuring fare payment) that can be carried out in a way that really just inconveniences the dishonest (instead of everyone).
Yes, and the atrociously slow service on the South End branch of the Silver Line and front door exit only on the Green Line are testament to this. Whoever thought front door exit only on the Green Line was a good idea should be fired and face a lifetime ban from working in public transit. Either that, or they should be forced to ride at the very rear of an outbound B line train and be forced to fight the crowd to get off at every other stop for eternity.