In the Drug and Alcohol Dependence study, within-lane weaving began to occur once the person's blood levels reached about 13 micrograms of THC per liter of blood. In fact, people with that level of THC had the same level of impairment as people with a blood alcohol content of 0.08 percent, which is the legal limit for alcohol in many states.
Nobody should be driving a vehicle when under the influence of anything that could affect their driving. Being stoned is much like being drunk, and could cause very sever consequences when driving. You shouldn't drink and drive, and you certainly shouldn't get stoned and drive. It's not fair to risk other people's lives and property like that.
We are only beginning to learn how dangerous it is to try to operate a motor vehicle while stoned. People should not drive while stoned because they can crash the car and hurt other people. People do not drive as well when they are stoned as they drive when they are sober.
I'm pretty sure it is illegal to drive while intoxicated or stoned or under the influence of any illegal drug. Anyone who does this should be arrested and charged. It endangers the general public. No state should legalize operating a vehicle while stoned or under the influence of any drug.