Marijuana has medicinal value! Shouldn't it be legal everywhere?

Some states are recognizing that marijuana has medicinal value and should be legalized. So many young people have criminal records that follow them throughout life because they have been stopped and arrested for possession of marijuana. If it is decriminalized, should their records be expunged? How should it be sold if it's used medicine? How should it be taxed? Should people be allowed to grow it independently?