I absolutely agree that the mentality of a terrorist suicide bomber and a mass shooter are very similar, but in the US, that mass shooter is much more likely to be shaped by reactionary right wing, nativist, and extreme Christian narratives.
Yes, at their rallies, Iranians chant, "death to America" . . . look at a Trump rally and the nonsense they shout. For that matter, the things people shout in a crowd at a baseball game can get pretty rough (Ever been to Fenwick when they play the Yankees?). In actual fact, Iran had nothing to do with 9/11, hasn't done much active threatening of US citizens since the 1980s, and is not a threat to us. Iran IS threatening Israel, but that's part of a larger problem that does not stem from Iranian extremism.
In conclusion, if you correctly see the danger of violent religious extremism, there's plenty of it here in the US to work against (note the Minnesota assassin!). And, yes, Iran is a terrible regime, mostly to its own people. Have you read Persepolis? It's a valuable historical reflection, a gut-wrenching family story, and a potent warning of the dangers of extremism in a democratic society.