Personally though, my fight is against a culture of car dependency.
Amen to that. Car-centric infrastructure has so many negative effects on society and the environment that go way beyond the issue of people driving while high. Reducing car dependency addresses so many problem at once.
The amount of people I see visibly fucking with their phones while driving (often at high speed) is really unsettling. In my day to day driving, I'm far more concerned about people on their phones than I am people stoned. They represent different hazards, but stoned drivers tend to be much more predictable.