Another way to look at it is, don't do the crime if you can't do the time. So yippee, now it's not illegal in some states.
In accordance with the rational standards of a free society a "crime" is an action which causes some form of harm to another or others. So If you choose to grow, or buy, and enjoy the effects of cannabis, a naturally occurring plant, how does that harm me or anyone else?
Please answer that question.
We can all sit back and watch the unintended consequences. Remember Colorado's increased car wrecks after legalization of pot?
A similar rise in traffic accidents, as well as other negative social effects, such as domestic violence, occurred when alcohol Prohibition was repealed in 1933. This effect was the anticipated consequence of sudden liberation after a long period of constraint. But also expected was the gradual reduction in booze-related misconduct that took place as the public became accustomed to its legal access to booze and the once illicit substance lost its allure.
A similar situation was seen in The Netherlands when it decriminalized marijuana in 1976. There was an immediate surge in use and associated negative effects, but that effect quickly subsided and today there is a substantial reduction in use by adolescents as well as adults.
What is not mentioned in any of the reports I've read about the increased pot-related auto accidents in Colorado is the exceptionally heavy increase in motor vehicle traffic caused by the legalization. For example, I live in New Jersey where marijuana is illegal. If it were legalized in New York or Pennsylvania there assuredly would be hundreds of thousands maybe millions of those who live in contiguous or nearby states and who would be making the trip monthly if not weekly. So legalizing marijuana in all 50 states will eliminate this obvious though unmentioned circumstance.
So I'm sure a substantial percentage of the increased accident rate is the result of the increased rate of traffic in and out of Colorado. It isn't only stoned drivers who are colliding, the crowded roads are contributing to the problem.