If morality was subjective, can a person be faulted for committing an act that he disagrees with the laws of his country to be theft?
If morality was dictated by society and culture, was Nazi Germany blameless in the Jewish Holocaust? How about Stalinist Russia on its "thought criminals"? These dictatorships clearly considered themselves correct in their actions. So given enough years, when Germany sees Jews to be enemies again or Russia its anti-Marxist, anti-Leninist detractors, the genocides of their history suddenly become right?
With all due respect, go figure.