To be sure, Assemblyman Tom Ammiano's bill to legalize marijuana in California is worthy of discussion.

Millions are spent on going after pot growers, sellers and users, to no noticeable effect. Any college student, aging hippie or suburban housewife who gets nauseous on aspirin can, with a little work, find a little weed for purchase.

Or, one can take advantage of an old "football injury," find the right doctor and get a prescription for medical marijuana. Any mid-sized California city with a moderately progressive population has at least one, and often several dispensaries.

While California struggles through one of its worst financial downturns in decades, one has to wonder: What is the motivation here?

On the one hand, the state would save money by ending prohibition of marijuana in two ways: 1) law enforcement and 2) incarceration.

Many law enforcement officials will say privately that their efforts to investigate, bust and prosecute people associated with marijuana -- at all levels -- is largely wasteful.

With prisons bursting at the seams, many of the low-level drug offenders could theoretically be freed under a marijuana legalization plan, if it were to include some amnesty for such offenders. This will lead to more savings for taxpayers, at little cost.

Granted, legalizing pot would only stop interdiction efforts derived from the state, as weed is unlikely to lose its standing as a controlled substance at the federal level anytime soon. However, given President Obama's stated "hands-off" approach to states with legal medicinal marijuana, it's not impossible to believe a similar philosophy could be applied to a state where all restrictions were lifted.

Yet one of the selling points for the marijuana bill is what will happen alongside the plant's legalization: heavy taxes on its sale.

Certainly, some level of tax makes sense. Marijuana is a drug, and other drugs are considered to have a societal cost for their use, thus a tax to compensate for that cost.

And it's reasonable to believe that some of the cost pot users will pay in a sales tax will be offset by lower prices for the core product, given that the black market that largely exists now for marijuana sets pot prices artificially high (no pun intended).

Still, all of this ignores California's recent history in trying to address a societal ill through sales taxes.

The best example of this is cigarettes. Since the late 1980s, voters and politicians alike have had few qualms about levying additional taxes on cigarettes. At first, these were directly linked to addressing ill effects from smoking, such as public health programs and awareness campaigns aimed at children.

That didn't last, however. Government officials at both the state and local levels began to realize that given the stubborn tenacity of smokers' habits, the amount of money coming from taxes was greater than any reasonable amount that could be spent directly on addressing tobacco's effects.

So they spent it on other things. And nary a cry of protest was heard from either major party, because after all, these are smokers. If they don't like paying the tax, they can quit.

That approach ignores a truism perhaps as ugly as a tar-blackened lung: Governments always find a way to spend money, and will come to rely on any source of money they get.

By linking cigarettes to spending for functions having nothing to do with the effects of smoking, governments, rather than curbing appetites for smoking by dissuasion through cost, in effect hooked themselves on cigarettes.

Look at one of the proposals voters will decide in May:  Take tobacco taxes from Proposition 10, which previously dictated they be used on children's health programs, and apply them to the state's general fund.

That tobacco taxes were paying for children's health programs could be seen as dubious enough, but for, in essence, textbooks, bridges and paper-pusher salaries in Sacramento? Illogical, frustrating and a glaring example of good intentions gone wrong.

To his credit, Ammiano's bill professes no lofty ambition in regard to using sales taxes from pot to address the concomitant problems legalizing it would create. Such revenues, under his bill, go right to the state's bottom line.

Bank on it: If marijuana is legalized and heavily taxed, it will be sooner, not later, before lighting up is seen as a necessary way for California to keep the lights on, literally.

And the phrase, "What were they smoking when they came up with that one?" will have a new, more lamentable second meaning.