The sorts of people who turnstile jump are likely to commit further crimes on the public transit system that more directly affect the ordinary people trying to use it legitimately. For this reason I specifically want the police to prioritize arresting and prosecuting turnstile jumpers - it concretely improves the experience of public transit for everyone.

This is the same reason that getting rid of fare-checking is bad - the sorts of people who are kept off the transit system by enforcing a fare, are not people you want to be in an enclosed space with.