There's an interesting point here. I suspect we would both agree that "driving has become safer in Colorado" because more people are choosing to be stoned at home, instead of drunk on the roads. However, I think there are still a lot of people stoned on the roads, and that driving would become even more safer if we could deter that through reliable detection. But it's possible that would be a wash or have a negative result due to re-tipping the scales in favor of being drunk and potentially driving. Obviously, that hasn't been tested, but I think it's worth shooting for an even better outcome, rather than just avoiding an overall bad one.