The entire argument for defacing license plates seems to be "tolls are expensive". So, 2 questions:

(1) Aren't roads/bridges/tunnels expensive to maintain? And doesn't that money have to come from somewhere?

(2) If a subset of drivers decide they're exempt from paying the toll... doesn't it just get MORE expensive for everyone else who now has to cover the difference.

These people are free-riding on the backs of those who pay the toll.