The law enforcers act as if they should influence the law itself. Possession of cannabis has been further decriminalized, but cultivating your own is still a felony. How will one obtain cannabis flowers? If they don't want to risk the felony charge, they can buy from someone who is willing to risk prison time.
Mike Harden and the rest say that people will be allowed to carry and use the substance at work. There is very little, if any, reason to believe that. The law says that employers cannot discriminate against cannabis users unless it impairs their work performance. If there is no impairment, what is the problem?
I don't believe the costs will outweigh the benefits of legalization. Cannabis is a safe and effective therapy for many conditions, including alcoholism and hard-drug addiction. The need for dangerous pharmaceutical drugs will also be greatly reduced. There will likely be a net benefit with Proposition 19.