He hates what he did to Fersia and the others and what he has to continue to do, because he can't quit. The only way to leave Level Five is through the belly of a beast.
And with Charlie and Glick's interference, that might just be McBrid's fate.
Read the exciting culmination of Feeding Fersia, Breaking the Brush Men and Rage of Rattus Norvegicus. Who lives? Who dies? And who gets to leave Level Five?