San Francisco and San Diego just announced that they will expunge thousands of marijuana misdemeanor convictions from years past. And people with convictions in other cities and states may be able to have them removed as well.

The law is a funny thing. Someone once pointed out that if two friends were walking down the street in 1933, one carrying a bottle of whiskey and the other carrying a bar of gold, the one with the gold would be a law-abiding citizen and the one with the whiskey could be arrested for a crime. A year later, the reverse would be true.

Similarly, people consuming cannabis in states where it's been legalized are performing an activity that they might have been arrested for in the past, but is now perfectly legal (at least as far as the state is concerned). That leads to a tough question: What do you do about their earlier convictions for smoking pot back when it was against the law? 

There are two schools of thought about this, both of which make some sense. Some argue that our understanding of marijuana's dangers and benefits has evolved and it doesn't make sense to keep denying people jobs (for example) because they once did something that is now quite legal. Others believe that if you break a law--whether the law is good or bad--you should be prepared to live with the consequences.

Law enforcement in California appears to be following the first line of reasoning. When using marijuana for recreational purposes became legal this year, the new law also allowed those with misdemeanor cannabis convictions to petition to have their criminal records cleared. However, the process is time-consuming and expensive. So the district attorneys in both cities just announced that they will take the initiative to expunge those records in their towns going back to 1975. They will also review marijuana-related felony convictions over the same period, with a view to possibly downgrading them to misdemeanors. Between the two cities, more than 12,000 convictions could be affected.

In Colorado, where recreational cannabis has been legal for five years, voters last year approved a bill allowing those with past convictions to have them expunged. In Washington, a similar law is before state legislators but has not been voted on yet. In Nevada, lawmakers voted in a law to expunge past marijuana convictions, but Governor Brian Sandoval vetoed it.

Recreational marijuana use has now been legalized in Oregon, Alaska, Nevada, Massachusetts, Maine, Vermont, and the District of Columbia, although selling it is still illegal in DC, and legal sales have not started yet in the New England states. Since most people seem to feel that continuing to carry a criminal record for doing something that's no longer a crime is illogical, that raises the prospect that past marijuana convictions will become expungeable in other states over time. 

Meanwhile, the U.S. Justice Department recently ended an Obama-era directive to refrain from prosecuting people for using or possessing marijuana in states where that's legal. That means new federal crackdowns on cannabis may be on the way. That leaves cannabis users and the cannabis industry in legalized states pretty much where they've always been--going about their business and wondering what the future holds.