The honor system works when there are social checks and balances that can be applied to punish socially for going against what's acceptable.
The whole point is that larger entities are shielded from some of these repercussions because of their size and power, and in some cases are almost completely untouchable by this system.
The legal system is there to catch extreme cases the social system can't feasible handle well enough. We don't just let murderers go and ostracize them, we incarcerate them and forcibly remove their rights. Some things are too important to allow social norms to be the ultimate arbiter of.
