There is a common misunderstanding regarding conflicts of interest; that the danger arising from a conflict of interest lies in the moral weakness of the man or woman with the conflict. That is, the danger is thought to be that the person may choose to compromise one interest on behalf of another when to do so would be evidently immoral, unethical, or unjust. In consequence of this widespread misconception, suggesting that someone has a conflict of interest is often taken as pejorative, as calling into question the person's character or motives.
This error has been promulgated, ironically, by people whose character really is in question. It is past time to remind ourselves of the real reason for avoiding conflicts of interest.
Conflicts of interest are to be avoided because they hobble judgment. It is a commonplace that the best motives may result in other-than-best decisions, for the simple reason that people can do right only according to the light they are given by which to see the right. The danger in a conflict of interest is simply that it filters the light. It can't fail to color one's perceptions. Knowing what is true in a situation is generally challenging enough when one is detached, and seeing clearly can be difficult even without obstacles to clear vision; a conflict of interest is such an obstacle to clear vision. It is a mental astigmatism.
The honest professions still honor this common wisdom, but the political and business class now brazenly flout it, in service to corruption. When we see Supreme Court justices making whoopee with political bedfellows, retired generals shilling for arms merchants, business tycoons rotating in and out of regulatory office, and politicians living large on the corporate dime, we should remember—and remind them—that it is no more defensible than the doctor who treats, the cop who investigates, or the lawyer who prosecutes his or her own loved ones. Our governmental and business leaders should avoid conflicts of interest, not because we think ill of them, but because we—and they—rely on their good judgment.