Shimon & Levi Destroy Shechem

Why did Shimon and Levi kill the people of Shechem? Were their actions morally justified? Morally imperative? And why do they serve as the prototype for the law of Bar-Mitzvah--the Jewish boy's attainment of maturity and responsibility?

Why would an irrational, irresponsible and legally questionable act serve as the precedent by which to measure reasonability and legal responsibility?

Calculating the bar mitzvah date, the privileges and responsibilities of the bar mitzvah boy, and laws and customs associated with the bar mitzvah celebration.