Perhaps the most fundamental requirement for a community's existence is for all of its members to know under what extremely limited circumstances one member may harm or kill another member. In addition to the obvious benefits to individuals, this protects the community from self-destruction. For this to work, members must also be able to reliably identify who is a fellow member and who is not.
A community can be a member of a larger community if its survival depends on other communities. The same requirement therefore applies, though the circumstances may be different from those for members in each community. Here, confusion could drive down the overall population, endangering all remaining individuals.
Power (the ability to influence the lives of one or more individuals) can be concentrated so much in an individual or group such that they effectively become a community unto themselves and apply different criteria to the remainder of their original community. Beyond a certain threshold of power, they may become unable to effectively know or control the consequences of their actions, even if they want to; in such a case, their power must be reduced below that threshold for those affected to avoid harm or death.
As a general rule, we could expect all individuals to avoid harm, which can be simply defined as a reduction in power that they don't initiate. Within the context of the community, there may be a level of power (such as the group average, or where basic survival is jeopardized) below which an individual is considered "harmed," regardless of whether the amount of power was restricted involuntarily. If there is the threat of harm, whether direct or through uncertainty, individuals can be expected to confront or avoid the source of the threat.
Several examples from recent news illustrate some of these points.
When President Obama approved the assassination of Anwar Awlaki, an American citizen, without going through a publicly known and acknowledged legal framework for determining the guilt or innocence of a citizen in a capital crime which is punishable by death, he effectively threatened the survival of every citizen using the power of the government. By losing a basic protection of membership in his community, Awlaki could be construed to have lost that membership based on judgment that the community as a whole had no knowledge of, or control over.
Obama himself has been subjected to unfounded claims that he is not a legitimate citizen of the U.S. by an arguably racist group of political rivals. Indeed, racism is practically founded on the notion that slight biological differences should properly define communities, a test applied by some people regardless of whether it is accepted or acknowledged by others who believe they are in the same community. African Americans have clearly lived with threats of harm in a myriad of ways, and the recent death of Trayvon Martin strongly indicates that they still live under the threat of murder in some parts of the country.
The global interdependency of the majority of people due to technology and cultural innovation makes it imperative that people become more, not less inclusive in their community affiliations if we are to avoid massive population loss. Our relationships with other species, defined largely by predation and despoiling of the resources they need to survive, threaten to impede their ability to maintain the habitability of the planet we share with them; they live under much greater uncertainty than we impose on each other, even in the most violent third world nations. We must therefore include them too, at least to the extent that we don't continue driving them extinct -- and potentially ourselves in the process.