No, it is not the role of the US to police every nation in the world. That's why we should not have invaded Iraq. The fiasco in Iraq cost us hundreds of billions in direct military expense, over 400 military deaths, and very likely our economy.
We must recognize our limitations and use our military wisely. The riots in Iran and the death of one girl is not a national security issue. We must closely monitor the situation and support the insurgents as much as possible.
This is a great argument for the 2nd amendment.