Unjust laws can and should be eliminated, but people using laws unjustly cannot. Speeding is a crime, but it is not perfectly enforced. Cops let family members go more often, good looking people, people they identify with, etc. Speeding is a just law that is not always enforced in a just way. This is always the case.
Ok how about murder? Guy murders someone by hitting them when he is drunk. Rich guy with a good lawyer and connections in the community gets community service, but the poor, black man with a pot possession misdemeanor when he was 15 gets life in prison.