Iran sponsors terrorism, but why should I care?

I saw a Congressional campaign negative ad (District not mine) saying the incumbent was wrong to support the Iran nuclear deal because Iran is the world's leading sponsor of terror.

That might be true. Iran funds Hezbollah in Lebanon and Hamas in Palestine. But...

What concern is that of the United States of America? Those countries aren't even in our hemisphere.

In the last 20 years, how many American casualties were produced from Iranian sponsorship of terrorism? How many were targets because they were Americans?

And if the sticking point is that Iran, Hezbollah, and Hamas are all opposed to Israel, would it be impolite to name the defense treaty the United States has with Israel?

I would say that it's clearly against U.S. interests to treat Iran as an enemy. But "U.S. interests" is only an illusion. Lots of people in the corridors of power have an interest in demonizing Iran:

• Elected politicians who want to list enemies they say they're keeping you "safe" from. Because much of the population still remembers the heinous Ayatollah Khomeini, they'll believe that any evil committed in the Middle East can be traced back to Iran.
• Defense contractors, who profit from the United States having as many overseas "enemies" as possible.
• Media companies for whom wars and rumors of war provide good fodder for their news channels.
• Think tank ideologues who believe America has an exceptional "mission" in the world that includes overthrowing every dictatorship and theocracy -- even at the expense of the liberty and prosperity of the American people.  

I do not excuse Iran's behavior in supporting terrorists. Nor do I condone its oppressive laws. But there are a lot of evils in the world I don't like, or wouldn't like if I knew about them. I bet I wouldn't like some of the customs in the jungles of, say, Indonesia. But I don't lose sleep over evils I can't control.

And the United States can't control, coerce, or defeat Iran in any conventional war that would involve invasion or occupation. So there's no reason for continued hostility. 

Open trade with Iran, and all countries. Declare neutrality in all foreign conflicts. Because further antagonism will make the U.S. culpable of further violence.