Let me answer you like this, in his hate to consume all undead in a holy fire the heretic uses the undead against the undead in an ironic kind of combat system. By turning a zombie against a necromancer the heretic is punishing the necromancer with his own creation. Also, the heretics hatred is contempt with the fact that the undead that he brings up or summons is destroyed eventually, burnt to ashes, making sure no one can ever use the undead creature ever again. He hates all undead creatures, but he will use them to his will seeing how he shows no moral system in destroying his enemies. But once the undead creature has served its purpose, the Heretic will undoubtedly make sure it is destroyed by his hand.
Let me answer you like this, in his hate to consume all undead in a holy fire the heretic uses the undead against the undead in an ironic kind of combat system. By turning a zombie against a necromancer the heretic is punishing the necromancer with his own creation. Also, the heretics hatred is contempt with the fact that the undead that he brings up or summons is destroyed eventually, burnt to ashes, making sure no one can ever use the undead creature ever again. He hates all undead creatures, but he will use them to his will seeing how he shows no moral system in destroying his enemies. But once the undead creature has served its purpose, the Heretic will undoubtedly make sure it is destroyed by his hand.