The retelling of what the scouting teams had seen made every one of the soldiers feel as if they were becoming one with nightmares. They were the witnesses to terrible things that definitely should not be. Especially when they heard about how the undead found any living thing to tear apart and use as fuel for their evil.
It wasn't that they felt bad for monsters, yet, it was the principle of respecting life. When the undead hunted monsters, it was for causing even more death for the sake of death. When a hunter or a soldier hunted, it was for safety, food, and the materials that would improve life for many. These reasons justified the cycle of life.