No the law does not justify unjust actions by authoritative figures. And the principles behind it are NO WHERE CLOSE to being identical. Don't forget, he is trying to compare smoking marijuana to the deaths of millions of people.
You both are under the HUGE assumption that everyone in the US believes marijuana poses no harm/threat and should be legal. Obviously, this isn't true, which is why it was made illegal in the first place. Chances are police officers believe that smoking pot is wrong. AND REGARDLESS: ITS AGAINST THE LAW!
Arresting someone for smoking pot is NOT unjust. It would be unjust if the cop saw you smoking pot, took you to a work camp, starved you to near death, then burned your body. Instead, they arrest, do the necessary procedures, hand you off to the court system where you can PLEAD YOUR CASE MIND YOU, and have a qualified judge decide whether what you have presented is right or wrong.
So don't fucking say the principles behind them are identical. Its fucking ignorant.