Right...I may have been misreading it, but I understood the contract with Sebastian to require that Ciel allow himself to be killed/eaten once he'd gotten his revenge; having gotten that revenge, Ciel's sense of dignity and pride (and possibly his feelings for Sebastian, whatever you read those as) require that he honor that debt without flinching. So I didn't find it as problematic as all that, but rather satisfying actually. But that may be just me.