Yes, marijuana crimes should be pardoned. Marijuana is a harmless plant that was criminalized decades ago as a way to persecute blacks and progressive activists. Imprisoning people who have used or sold marijuana costs states millions of dollars each year. This money would be much betters spent on infrastructure projects.
I think that most Americans now understand that marijuana is basically harmless, and it is very safe if it is well-regulated. Therefore, it shouldn't be illegal. In the mean time, people who have received ridiculous sentences for marijuana-related crimes should be pardoned. One exception I would make, however, is for driving under the influence of marijuana. Driving a car is a major responsibility, and anyone who drives under the influence of any drug should not get off easily.
Crimes related to illegal use of marijuana should not be pardoned. Although many states are making usage legal, the people still knowingly committed a crime at the time. Litigating these cases again is both costly and time consuming. It would require reviewing many cases, which will cause a backlog in the justice system.
Marijuana often causes more driving accidents than alcohol. The only reason that it isn't caught more often is that it is harder to detect. Marijuana still hurts a lot of people. It is not regulated, nor is it productive. A person high on marijuana can often cause harm to others, and when this happens, the person should be held accountable.