Sounds like a good idea. Transport for London already does this.
https://fr.wikipedia.org/wiki/Gratuit%C3%A9_des_transports_e...
It works partly because the fines are relatively significant and levels of public trust and integrity are likely more universal, so there are few "Schwarzfahrers" (fare dodgers, literally "black travelers").
Caltrain has the same "honor" system, but conductors often do proof-of-payment checks.