I mean, yeah they were trolls and ogres. But they hadn't actually done anything wrong as far as Arthas was aware. They made for the perfect scape goats due to their job and various races. I don't blame the soldiers as they had plenty of reason to believe Arthas.
Arthas however is definitely not innocent there. He lied to his own troops, destroyed his own ships, and as a result ended up dooming the whole expedition into Northern.
As for Stratholme, I mentioned it because it's clearly the breaking point for him. I don't necessarily disagree with the choice was made, but I believe the events that followed he was not of sound mind.