Dealers don't want marijuana legalized because they'd lose their business. Marijuana would also be much more expensive.
Actually legalization would likely increase supply much more than demand. Not only would the price come down, but so would the profit margin. In addition, if the tax on legal marijuana is sensibly set (sensible from the viewpoint of being high enough to raise revenue but low enough to discourage evasion) a good chunk of the profit is likely to absorbed by the government.
The government can tax it all it wants, but the second full legalization comes, the whole dispensary system starts to fall apart. Weed is a weed. The true cost to grow it in an environment where it's legal is going to be incredibly low.
