Iran supports all sorts of Islamic terrorist organizations such as Hamas, Hizballah and Islamic Jihad.
The moral obligation to kill the 'occupiers' of Muslim land is one of the historically stronger ‘laws’ of Islam. This is only one of the reasons why we are at war. I like to use an example:
A bunch of Muslims seize a Catholic church in Chicago, IL. The Catholic Church owns the land, but they do NOT send an army to kick the 'occupiers' out. The United States government sends in the army.
Clearly, Iran feels that they need to enforce this Islamic law. In addition, Muslim ‘land’ and ‘waters’ are permanent. Another ‘authentic’ Islamic law is that the penalty for leaving Islam is death. Once someone or something becomes Muslim, it cannot revert back.
I am guessing that many who believe that the wars in Iraq and Afghanistan were a mistake either do not understand or underestimate the importance of these ‘laws’ within the Islamic world.