If you can remember to scan when you get on (which doesn't fit the "normal" behavior of a paper ticket either) then you can remember to scan when you get off. It's no different than BART, the main difference is BART funnels you through an exit. If you have a round trip commute, then you are going to enter and exit at nearly the same points.
Once the density of people per square mile is over a certain point, the usage of cars contributes to a tragedy of the commons, inconveniencing many of the residents in the city for the benefit of few. New York has been one of the more aggressive cities in removing parking and closing down roads to car traffic and it has greatly improved the quality of life there for residents.
London's Canary Wharf district is able to support 100,000 jobs with only 3,000 parking spots. San Francisco's problem is that it hasn't yet made the city sufficiently convenient for humans on foot and bicyclists at the cost of inconvenience to drivers.