Which is a fundamentally flawed argument. By becoming a vigilante, you've already implicitly admitted that the machinery of the state doesn't work be it due to incompetence, inadequacy or corruption.
The prmary problem is this fetish for Batman being Judge Dredd and being all "I am the Law!!". I'd be much more tolerant of his no kill rule if he'd just admit to a personal aversion to killing instead of continually desperately trying to justify it legalistically when his very existence as a vigilante crimefighter shatters any sort of moral or ethical authority that could possibly extend to him.
Even his once offered aside that "We don't kill because that would make life difficult for us with the police" is a preferable justification to "we don't kill because the law says it's wrong so we must obey the law".