Assuming that taxing marijuana could raise significant revenues, the question becomes "Who gets the tax money?" Localities might be the first innovators, but if there proves to be significant income I would expect the states to intervene to take the money -- to be followed by the federal government looking to take the lion's share. If they all try to tax the stuff too highly they will almost inevitably over-tax and lead to various problems. But no-one will want to sit out when such a handy new source of revenue is coming on-line. Because of marijuana's current status, I would expect that the federal government would make a big argument that it should be able to pre-empt. States will no doubt try to protect "their" markets from other states, and cities likewise would probably prefer a local 'sales tax' model as opposed to a federally regulated paid license system.
Couldn't an economic argument be made that keeping marijuana illegal is actually more economically beneficial than legalizing it? This is probably almost certainly true for communities/regions that currently make a lot of money from the illegal business. What will happen to Northern California when 'commercialized' "BC Bud" is imported for pennies a joint? California might lose its revenue from marijuana, only to watch the feds slap a high tarrif on imported pot to suck up all the money that is left in the trade.
Legalizing pot might be a good way to "get the turkey on the table." But with literally dozens of slobbering, hungry, interests looking to get "their share" the carving can be expected to be a mess.
