I grew up in a large city without a car. Public transport was my primary form of transportation until I got a car in my late 20s. I can't remember a time wherein the lack funds for a fare was used as a pretense to kick 'troublemakers' off of public transportation.

The underlying 'trouble' that makes someone a 'troublemaker' (e.g. aggressive panhandling, disruptive behavior, public drunkenness, etc.) are still reasons to be kicked off public transportation irrespective of how much the fare is.