Wouldn't be a bad idea. E.g., here in SF, the fares bring in $200M/year, and Muni's budget is $1.2B/year (approx numbers), which means, for every $2 charged by fare, the City has to put in another $10. Making it free would just cost an extra $200M/year, which is within the realm of possibility for a City with a budget of $14B/year.
