The Washington State initiative does not "legalize" pot and is not a good model to follow. Because to grow recreational pot, one must secure an expensive license from the state, costing $250 application fee and $1000 annual fee. The state liquor board can turn down applicants for whatever reason it sees fit.
This type of cronyism is a recipe for corruption and large-scale growing. Applicants may learn to bribe officials to get the license, and to pay the high fees and bribes, must do a large grow. Such large grows are a security problem, acting as a magnet for thieves.
I sell new technology lighting for indoor plant growth. What if the large crony growers boycott my store? Where does that leave the person who wants to do a small grow?