Think of loyalty as a kind of relational glue.

The roles evolve over time: juries once made determinations about law; nowadays, they are supposedly limited to making factual determinations. A good move? All along, however, we will, be employing and refining "established" values in new contexts, with the possibility of restructuring them in some way.

Structurally I don't see a fundamental difference between what we may reasonably expect of police and doctors - though obviously the fact that doctors are generally pursuing life-saving activities and police may be engaged in life-threatening activities may lead to differences in how we construe the moral limits to their roles.

Loyalty saves us from the self-advantaging compromising of important relations - such as friendship, marital and professional commitments, group memberships, and so on. But as the Aristotelians would put it, its expression requires phronesis - wisdom not to allow it to compromise other important virtues ,there is something to the ancient doctrine of the unity of the virtues. I believe that is true of all virtues, but especially of the executive virtues - such as industriousness, sincerity, conscientiousness, and courage - which may become detached from substantive goods.

My mother thought my inclinations would do well in Law, but I was too shy and deliberative - slowfooted - for that, so I determined to be an English and German high school teacher. In my first year of university I had one subject to "fill in" and chose philosophy against the advice of my counselor. My university teachers in English and German were totally uninspiring; philosophy was wonderful and my results showed it. I chose it and basically backed into a situation in which only a philosophy career seemed a viable option. I've never regretted it, but there was a lot of serendipity.

It is odd that a value/virtue that plays such a central role in dramatic literature has played such a small role in philosophical writing. There are probably a number of reasons, but I think that a predilection for a certain kind of individualism is a major one. Others might include the fashionability of consequentialism, the idea that loyalty has more to do with sentiment than reason, as well as its proneness to corruption. The revival of interest in virtue/character as distinct from rules/principles has also created space for a renewed, if hesitant, interest in loyalty.

In later years, when I started working in police ethics, I was professionally drawn back to the topic but as well was better able to see two sides to loyalty - its importance for certain central human relations such as friendships, but also its corruptibility in the sense that loyalty could be invoked against other moral constraints: it sometimes function as something of a moral Trojan horse, undermining other moral considerations.