Question

Managers should run a business ethically because

Answer 1

Because it is the right thing to do.
Before even considering the economic aspects on why they should run a business ethically, they need to first consider the morality aspect on treating other people with good intent.
On top of that, running a business ethically will improve's consumers' loyalty toward your company which will make your sales become more stable each year.

Answer 2

Managers should run a business ethically because it is the right thing to do.
They should do things ethically just because they are afraid of punishments and repercussions. Instead, they should understand the importance and moral value of acting ethically because they will set an example and then the employees will be ethical as well.