So then you do understand why he should be ethical: being an unethical person is a bad thing.
> why should he take it in the absence of laws that force him to or professional/reputational damage to him.
If the only reason that you behave ethically is because you will suffer consequences if you don't, then you are not ethical. I'd hope that such a person would have problems looking themselves in the mirror, but I know better.
So then you do understand why he should be ethical: being an unethical person is a bad thing.
> why should he take it in the absence of laws that force him to or professional/reputational damage to him.
If the only reason that you behave ethically is because you will suffer consequences if you don't, then you are not ethical. I'd hope that such a person would have problems looking themselves in the mirror, but I know better.