One of the problems with many of the conflict of interest codes is that they do not speak of or consider duties. For the purposes of my discussions a duty is an implicit or explicit obligation that is owed to a third party. A duty has a specific and determinable beginning, its terms can be objectively determined by a third party and it may or may not have an ending. An interest is a direct gain or benefit for a person or organization. The interest may be actual or perceived by a third party.
Rather than engaging in this separation duties are subsumed into the general category of 'interests'. The problem is that this places implicit or explicit obligations that a person owes to a third party on the same level as the personal interest that is referred to in the MacDonald definition.
Frankly resolution of a conflict between a matter of personal interest and a specific duty should be fairly easy if they are considered as separate items - performance of the duty trumps the interest. The more difficult issues relate to conflicts between duties (which duty is fulfilled and which one is abandoned) and conflicts between interests (which interest prevails). Coming up with principled answers to these questions can be very difficult.
The failure to think in terms of duties when drafting conflict of interest codes leads to a failure to establish a hierarchy of duties and interests for individuals who are subject to the code. For example it would be very easy to start a conflict of interest code with the following statement:
Each individual who is subject to this Code has a positive duty to ensure that the best interests of Organization are the paramount consideration when taking any action; making any decision; dealing with subordinates, customers or stakeholders; or entering into any transaction.
You will note that I use the word 'paramount' as opposed to 'only'. The reason for this is that individuals can often have other duties (statutory obligations, professional reporting etc.) that may also have to be considered. Any code has to keep a place for the consideration of other duties to third parties.