Lately, whenever I talk or write about the ethic principles of permaculture, I usually add a fourth principle, or rather, I "upgrade" one of the design principles: Diversity. Caring for Diversity may come very natural for people who have adopted the principles in their daily life, but for many people it doesn't. From a permaculture perspective, Diversity is just part of the definition of people care and earthcare, but you won't find that definition in any dictionary. Diversity is often feared and discouraged, or considered unproductive. In farming or forestry or just about any commercial activity monoculture is still the norm. On a community scale you may do a good job caring for people and the environment, and taking care that everyone has a fair share, and still end up in a monoculture - filled with racism, conservatism, intolerance toward different ideas, sexual orientation, etc.
Diversity is also a key element in the transition movement. In every speech Rob Hopkins gives, he stresses the importance of Diversity as a key condition to attain resilience. In the Web of Life game we learn that diversity is what makes the web strong and resilient.
So far I treated permaculture and our transition initiative as two different stories, closely related but different. Upgrading Diversity to an ethic level helps me personally to view the two stories as one.

Care for People
Care for the Earth
Provide a Fair share
Embrace Diversity