Harmony should be achieved by accepting people's individuality and preventing conflict by getting rid of the source of the problem.
Many people are voilent and aggressive because they feel a need to prove themselves, or feel excluded from society (it is much easier to destroy something that you have not been involved with building). Maybe our verbal Aikido starts by showing that each person is valued and respected and has an important role in society.
To me Aikido training does this in itself and enables very aggressive people to gain confidence in themselves whilst building respect for others.
In terms of forcing people to comply with the law by using martial arts - that is a different story. We must remember that our right and wrong is very subjective. Law is necessary for society, but in the words of a famous horse-trainer; you should never use physical force to make an animal or person do what you want them to do.