Do you know any Americans dating any Iranians or marrying them?
Out here, my sister wasn't the only case. When I would bring up the story of my sister in conversation, I would almost always get back that they at least know someone who had the same experience.
Like I said, best to stick to marrying Americans. Anyone of any nationality that are born here are more likely to be equally yoked with you.
But I also recognize not all Iranians are alike, any more than all Americans are. Perhaps we've just managed to travel in different circles. (I'm of an age where "dating" is no longer a common practice, for example...)
And this I will agree too: Marrying within your culture makes for fewer difficulties than marrying outside. (I want to explicitly make that "culture," not "nationality," because even within a country, including the U.S., there can be significant cultural differences. Though I lived in CA at the time, I preferred my down-East Yankee girl.) But I've seen couples from quite disparate backgrounds make a successful go of it regardless.