Raze could see the blinding, unadulterated rage in Allen's eyes, and in a lot of ways, he felt it was wrong, perhaps even hypocritical, to try and stop him. Raze himself had felt that same consuming rage before, a feeling that drove him to do whatever was necessary to achieve his revenge. He understood that primal need for vengeance.
The undeniable issue, however, was that regardless of the chaotic actions Harvey had taken, Raze desperately needed him and the powerful members of the Dark Guild to achieve his final objective. Varkos and Mordain were both already dead, a harsh, unchangeable reality. There was nothing that Raze could do to reverse that. As long as Raze could keep Harvey on a tight leash, controlling his impulse to kill, he could stop Harvey from killing others, and that absolutely included Allen, who was too valuable to lose.
