The Iranian government has frequently reference a goal of destroying Israel, a sovereign nation, and referred to the US in very disparaging (and biblical) terms. That doesn't justify direct attack, but it also isn't diplomatic.
That's completely unfair to Iran. They had IAEA inspectors in their country and they were negotiating with the US (a nation who has put crippling sanctions on them).
Then a country that doesn't have IAEA inspectors bombed them, killing the people that very people who were negotiating with the US. Their message since than has been reasonable; "we won't negotiate while Israel is attacking us".
How much more diplomatic would you like them to be? They can't just roll over and take it, or they'll be finished.
Are you aware that Iran approved of US invasion of Iraq in the Gulf War? It even allowed the use of it's air space.
Are you aware that Iran was the only country excluded from the Madrid peace talks of 1991 between Israel and Palestine? To counter this exclusion, Iran strengthened it's ties with Hamas and Hizbollah.
Iran is not some insane theocracy seeking of everyone's destruction. The regime is bad for the people, but self-interested just as any other, and benefits very little from full exclusion.
Apparently also Belgium , Italy, Turkey, Germany have the same type.
You could just as easily say that doing regime change in a country will make them hate you, or that backing out of deals will make things worse, or that Israel can shape US policy at their own whims.
Yes, Iran had a stupid nuclear strategy. But that is only a minor part of this story.
