Fare-free transit just makes sense. We want people on the bus or train instead of driving. So it should be the easy choice. No scrounging for cash or filling up a card, just hop on.
It's more sustainable, it reduces traffic deaths and air pollution, and it makes cities more livable to have fewer cars.
And: there's nothing radical about it. We've got free parking frickin' everywhere even though cities' costs to provide clean well-paved asphalt are far from free.