The way I see it is that at this point all the money (billions as I'm sure we all know) and effort spent on prohibition aren't keeping US from smoking it, it is just keeping a few million (at most) from smoking it.
But really If we look deeper we also all realize that it is just a way for a few companies to make bank by eliminating cheap and viable competition while the taxpayers get to foot the bill. So as we can see the whole thing is rooted in corruption and cronyism all for the sake of some good ol' boy network. Laws are supposed to protect the people, not enable a few to make extravagant livings at the cost of the taxpayer. Running an operation like this is bound to either fail or be very unjust, and in this case it's both.
Also consider that if legalized anyone with a green enough thumb would be able to bypass going to the local weed store, setting good old capitalism to fail itself. So really, like everything else, it all boils down to money and who gets the most of it, not what's best for us, or for society, not what's best for the taxpayers, what's best for the money machine.