They were well within their right to shoot at the Americans, who were only in the area to provide aid for Saddam, who was gassing Kurds and threatening to gas Tehran. Expecting the Iranians not so shoot back was foolish, and shooting down that airliner in retaliation was plainly barbaric.

The aftermath of the incident has no bearing on whether the Iranian reaction to the intrusion was rational or justified. The order of events does not support such a line of reasoning. What you are basically saying is that nobody should ever shoot at Americans no matter where they are or what they are doing, no matter the current military or political circumstance. Ridiculous.

To be clear, the shooting down of the airliner was a mistake (it was misinterpreted as an attacking F-14). It was not done in retaliation to anything.

It is not clear at all. That version is heavily disputed, and reflects only official US Government's view.

Just to make it completely clear (I hope), I'm saying a country should not shoot at entities of another county it is not in a hot war with.

And I think that is a fine principle, but an unreasonable expectation.