Originally Posted by
M-Ra
Betraying the Mercenaries was pretty shit, but that were only Trolls, so yeah. At least he did something instead of waiting what will happen like the Rest of the Alliance or fleeing like the Horde and in Stratholme, he was right. Most of the People in Stratholme were already doomed, everything Arthas could do was saving them from becoming Members of the Scourge and letting them die as Human, What would you prefer, becoming an eternally damned Undead and be mindcontrolled to attack and kill everything you love and hold dear or find piece after one, single Blow of the Warhammer of your Prince?
And Frostmourne was back luck. He was ready to sacrifce his own Soul for his people, he couldn't know that this was a trap by the Scourge itself. It's like saying "Oh, it's Darions own fault that he became an undead Death Knight after killing himself in the middle of Scourgeland".