Pretty sure killing all the enemies just turns the rest of the world into enemies.
Before you ask "how's that going", remember that doing nothing wouldn't result in a satisfactory answer to that question either.
The idea that "killing the enemies turns the rest of the world into enemies" is absurd. Other countries wouldn't follow the Iranian regime into martyrdom. What would be the reason: "we don't like war"?
Nobody likes war, but also nobody likes evil dictators emerging on this planet and repressing 90 million of its inhabitants, and waging industrial scale terrorism offensives beyond its borders.
She sat they killed some of those rebels, it would have sparked more rebellions. The difference was political power, even in defeat. Mercy is a big part of survival.
It's a bit like law enforcement. If there's no police, criminals are everywhere. If there's too many police, corruption becomes the standard, along with police brutality and profiling. You can never get it down to zero, just low enough.
And these countries are supposed to be Iran's closest allies due to having a common enemy.
Not sure where you get the idea that people don't care who they are friend with. They absolutely don't want to be friend whose culture is considered as disgusting.
They may form an alliance due to having a common enemy but in practice the alliance is just checking a box.