WoW's moral judgment is the most void of all morals. They just look at the killer and completely forget about the victim.
When you let a killer loose out of mercy. You are returning to punish their victims.
Besides there is a theme. A trial is to find out if someone is guilty. But in this case it is already known that if.
To give an example:
Every time Anduin forgives the Horde he stains his hands with the blood of the alliance that the Horde will shed again. He spits on the graves of those who died to stop the Horde.
With the peace treaty without claiming anything. Anduin did nothing but insult all the Kaldorei killed in Teldrazzil.