Petraeus works to halt foreign fighters.

Plus this blaming Iran for everything is just foolishness.
Reb, you are right, what threat do they pose?

Aren't these foreign fighters similar to the ones fighting the Soviet union in Afghanistan in the 80's? if so, I seem to recall them being from everywhere not just one nation.

Iran makes the Sunni Middle East nervous because it is a source of Shia pride and solidarity and it aids shia militant groups. Likewise the Sunni majority make the Shia minoroty nervous due to the religious schism and history of conflict.

Iran can be a threat to our "interests" to the extent we choose to take sides in this fight.

They can hit us asymetrically in many places around the world. They also have some dangerous anti-ship missiles that could be deployed in the Persian Gulf: Supersonic "Moskits."

As far as the idea that Iran is going to conquer the United States or present a serious or sustained conventional military threat beyond its immediate border regions, that is propaganda.