Well you'd better raise the tax some more to pay for NYPD overtime then, because the bus drivers aren't going to determine who can ride the bus and who can't. You are aware that MTA has a lot of busses, right? Like I said, I like the idea of 'free transit' on ideological grounds, but it just doesn't work the way you might think it does in practice. The other issue that BART found on free days was that it became a kind of rolling party for kids; truancy was up 30% on those days :-)
I'm personally not bothered by either of these issues, but huge numbers of people complained about how the transit system essentially became a magnet for people with nothing else to do -- and these days are in the summer! Just wait until it rains or snows ...
Back to my previous point: you *cannot* "fix" a complex problem with a "simple" ("so simple only an idiot would be against it!") solution.
/jordan