Ah, I misunderstood. In any case, onion traffic is not flagged as such, so nobody but the last hop would even know that onion traffic is being passed. Allowing

Ah, I misunderstood. In any case, onion traffic is not flagged as such, so nobody but the last hop would even know that onion traffic is being passed. Allowing the last node to kill the whole circuit seems like it would cause routing problems and/or contribute towards deanonymization, as would flagging onion traffic at every step of the journey.