Technically no its not morally wrong to not kill someone for the sake of protecting potential victims if batman ever did kill someone it probably be in a indirect way like we almost saw in the Dark Knight.
Joker's going come on come on knowing that the bat would act through this process but at the last second Batman decides not too.
@Alex if you went back in time and killed Hitler do you know what is most likely to happen. Someone worse would come along. and if you killed him someone worse would come along. Until the world erupted in a nuclear holocaust. It's the philosophical butterfly flapping its wings