The bloodline Primarchs could not help but feel a sense of defeat as the Neo-Demon's monstrous willpower assaulted them. Issac and Salomon had the strongest sense of justice among the Primarchs, but even they had to reach a certain level of compromise with the universe's dark side.
However, Zatiel was not willing to do that. No matter the background or status, he would hunt down all those he considered had fallen into depravity.
"What is your definition of evil?" Salomon was the one that made that question, but it was something that affected everybody. Evil is not something that can be so easily defined, especially in a universe where the idea of Might is Right had ingrained deep into almost all forms of civilization.
Who among the Primarchs had not to kill billions of lives in their path to power? It was an unshakable truth that to rise into a higher stage, you had to do it over the bones of your enemies.