I'm trying to figure out legal implications of something that is not illegal...but unethical. For example if an attorney enters into a technically valid contract....but a part of the contract promises something that is unethical for the attorney to promise, according to the ABA model rules, is it still a valid contract?

My current thinking is not all ethical violations are illegal in the eyes of the law. I do understand it could lead to other consequences such as being disbarred. I keep going in a circle! Any advice you can give me would be appreciated.