That assumes there is no internal "don't want to fuck someone's life up without cause" incentive internal to the individuals (i.e. that assumes psychopathy on the part of everyone involved in the justice system).
That we have police and courts at all assumes that people harm others without sufficient cause. Any argument that we need no external incentives for everyone involved in the justice system to do the right thing is an argument that we don't need the justice system in the first place.
What I meant was that to assume there was no incentive was to assume complete psychopathy on everyone's part. What you are saying is that while the basic empathy incentive may exist, it isn't enough. I agree with that just fine.