"It certainly did not help that the United States had stood idle while the regime slaughtered tens of thousands of its opponents, before making the attempt,"
"Now, before we go forward, I want to clarify a few things. First, none of this is a defense of the Iranian regime, which is odious. That said, there are many odious regimes in the world and we do not go to war with all of them. Second, this is a post fundamentally about American strategy or the lack thereof and thus not a post"
Let's look at a scenario. I'm a local policeman who jails everyone in my neighborhood who steals from others, except one person that I allow to steal anything they want, whenever they want. When a victim of their theft tries to take their property back from the thief, I stop the victim and jail them for theft, because they tried to take what is now the property of the original thief. Some people say that I had no right to jail the victim for trying to take back what was originally theirs from the thief. Other people cite that it is technically theft and that someone else constantly getting away with theft does not mean that the policeman shouldn't stop this current case of "theft". Whenever the victims tried to do it the proper way and report the thefts to me, I did nothing.
Should the society trust me to continue doing law enforcement? Of course not. They should immediately replace me, and if that's not possible, they should exile me and organize themselves into a militia and enforce the rule of law on their own.
Going back to the real topic, USA has no moral right to intervene on the basis of punishing "slaughter" when they themselves are in the business of slaughtering people worldwide if it's in the business interest of its elite, and supports other countries slaughtering if it's somehow to the perceived benefit of the USA's leaders. The rest of the world should never allow it given USA's historical record, even a recent one.
That the USA allowed Gaza to happen has put an end to the idea that Americans are the good guys and only do things that are good. The rest of the world sees this, even if heavily propagandized American citizens cannot, for whatever justifications they give.
And the USA's inability to reign its security partners in when they commit genocide has put an end to the idea that the USA has any actual weight in its diplomatic efforts.
The world is moving on from American hegemony - we will have to look to others for help in stopping America and its partners' slaughtering.