Why would we want that?
I don't want fellow employees legally stoned so they can jeopardize workplace safety and the performance of the company.
We also don't need more parents stoned so they cannot take care of their children.
Children don't need the OK of the government to go ahead and begin using drugs by following the example of their own legally-stoned parents.
Why don't you just make up a list of everything you want, and the government will outlaw everything else.
If drugs are legalized, companies can still require that you be sober, the same way they do for alcohol.