I have to disagree with you. "Publicly-held companies" don't encourage immoral behavior. People encourage immoral behavior. I know that some folks like to think of people as "basically good", but I don't think history has held that out. Humanity has proven time after time that regardless of the social structure or organization, their tendency for immoral behavior pervades each one.

"We did it for the shareholders" may be a unique excuse in the realm of organizations, but governments, churches, companies, school boards, communes, etc all suffer from problems like these. The difference with public companies is that folks can vote with their dollars, or in an adequately free economy, can band together and compete.