why am I supposed to distrust/hate Iran?

With Donald Trump sashaying around the Middle East, a question I have yet to hear a clear answer to crops up in my mind: Why am I, or my country, supposed to hate Iran? Seriously, I don't know. Is it because Israel needs a scape goat as Hitler needed the Jews? I really don't know but even a quick Google query yields paragraphs (admittedly biased, but how biased?) like

...Iran is by no stretch of the imagination a serious threat to the United States, Europe, its Arab neighbors, or Israel. At best, it is a third-rate military power with a dysfunctional economy who’s entire GDP is only a little over 60 percent of the US military budget. The supposedly terrified Israel has somewhere between 80 and 200 missiles with nuclear warheads that could send Iran back to the Stone Age in minutes. There is no evidence to suggest that even the most fanatical elements in the Iranian government are suicidal.

If it's the nuclear weapons capability, why is the United States equally wary of Israel?

Seriously, is there some reasoning in the middle of all this or is it all agitprop?