I’ve run the quest twice. And you can look at the quotes in the wiki. In no way do the guards make any objection to experimentation on him. They are disgusted by the sight of someone being turned to ooze. But the never try and stop you, or even make any suggestion you shouldn’t.
There is nothing that what the Captain says that says he has any objection to experimenting on the prisoner other than the experimenting failing. And, in fact, when he sends you to make up for what you have done, it addresses his concern about being attacked by the blight.
I mean, not word is said about experimenting on people being wrong. Nobody is punished. Nobody does anything to stop it. I have to say, if the Alliance considers experimenting on people to be a horrible crime, there is little sign of that here.
I have to say, a leader protecting his people is not list of “selfish” behavior, especially if the alternatives are futile acts.
Personally, I don’t think war crimes committed by Arthas against Alliance citizens should count as War Crimes against the Horde, since the citizens of Lordareon weren’t part of the Horde when he committed them, and he was largely a rogue agent beginning at the Culling of Stratholme.
A’dal and the others were simply following a vision that Velen had about Lady Liadrin and the Blood Knights and their eventual redemption. Which ultimately did come true