How does that justify threatening genocide and the end of their civilization?

Having previously lived in Iran for 4 years, I know that the Iranian regime is very oppressive and cruel, but all the US has done is fuel them. They thought that bombing Iran and killing Khamenei would lead to civil war and a collapse of the regime. It did none of that and invited retaliation. In return, the US just made all of the regime's claims true by making the very threats the regime had been saying were the US's intentions for the Iranian people.

Being precise and consistent in messaging that the goal was regime change would've been the absolute bare minimum bar for lending credibility to this war.

Trump is not particularly intelligent.