I've not been in a place with a functional transit system where fares were high enough to prevent disruptive people from boarding. I've seen rich people get onto Acela trains obnoxiously drunk.

I have, on the other hand, seen transit operators (bus drivers, mainly) kick people who had paid fares off for being disruptive. The definition of "being disruptive on the subway" does not seem to be the barrier you think it is.