The answer to your question can be found in Chapter 13 of this excellent novel, after Okonkwo has been banished and Obierika is sitting down and thinking about his friend's punishment. It is clear that he feels somewhat ambivalent about the kind of punishment that people face when they committed a crime either in ignorance or inadvertently. The situation reminds him of his twin children that he had thrown away. Note what he says about them:
Why should a man suffer so greviously for an offence he had committed inadvertently? But although he thought for a long time he found no answer. He was merely led into greater complexities. He remembered his wife's twin children, whom he had thrown away. What crime had they committed? The Earth had decreed that they were an offence on the land and must be destroyed.
Clearly, Obierika questions such "justice" and punishment when the people involved have no responsibility or choice over the way that they offend Earth. Just as Okonkwo killed by accident, so his twin children had no other option but to be born as twins, yet both were punished indiscriminately. Obierika's questioning shows how unsatisfactory he finds this arrangement.