Community.
The word that is right up at the top of my top ten list of "exceedingly ironic causes of pointless, nasty sniping". Bonus irony points for when it's in the context of a group that emphasises some level of communal values.
So what does the word mean to start with?
According to the Oxford English Dictionary:
2. Common character; quality in common; commonness, agreement, identity.
3. Social intercourse; fellowship, communion.
4. Life in association with others; society, the social state.
(There are more definitions than these; this is all of those in the first section and gives, I believe, a decent overview of the relevant uses of the word for purposes of this essay. For further information, consult your own bloody OED.)
So the general case is 'shared stuff' -- that stuff may be property, or it may be something more abstract, something like identity or a trait or an agreement. It may also be an intangible of a particular type of interaction or fellowship, but, again, that is a variety of 'shared stuff'.
So the tremendous arguments that come about because of 'community'? basically, they boil down to what stuff is shared. And what that means.
At its broadest, most general, and least useful level, there is a shared-trait meaning of 'community'. Here there is no meaningful interdependence (as in definition #1), just 'common character', which may not even be terribly meaningful as a descriptor depending on how people define that common character. Consider the community of cooks -- some might define that by professionals working in the field, some might include hobbyists at various levels, all the way down to people who can just about boil water. The lines get drawn in different places, depending on the criterion of what stuff counts as shared stuff.
To qualify as a member of that sort of community, one just needs to be adequately described by its descriptor. It doesn't really mean much in the grand scheme of things; it's just an adjective. At the same time, it has no obligation of any sort plausibly attached to it, though one is almost certain to come across at least a few people who are convinced that one's going about it all wrong.
One of the common ways people pick fights over going about it all wrong comes about when there's a disagreement about the definition of the adjective. In some cases, this is a case of drawing different lines in the grey area. In other cases, someone flatly has their facts wrong. Sometimes this can be fixed with an argument. Sometimes it can't. Some people are willing to protect their contrafactuals with their lives.
This matter of shared trait is not a terribly meaningful form of community; thus, the question of meaning comes into the picture. At this point, community becomes not merely a matter of shared traits but also shared obligations: to the community itself and to its members.
I would suggest that the value of being a member of a community depends on the obligations people have upon becoming members. A community that is purely defined by an adjective with no additional responsibility entailed is not one that will provide a lot of upkeep or support for its members solely because they are part of the community. One where a great level of support is expected from people as they join the community means that people can count on getting that level of support when they need it.
I would also suggest that even communities that are mostly defined by group membership or group identification often have additional obligations, which are typically considered minor or even things that don't register as present except when someone believes that they have failed to be kept up. For example, one might argue that a basic obligation of a pagan community is not to act in such a way as to exclude the practices of other pagans from what is considered "pagan". The arguments in reconstructionist circles about whether the reconstructions are pagan derive in part from a feeling that that obligation has been failed -- that "pagan" has been defined in ways that exclude or are even actively hostile to the practice of reconstruction, whether because it rejects some principles or ideas directly or attempts to define paganism positively as something including things that do not have a part in reconstruction. (Often such positive definitions are matters of "paganism" being mingled with "religious witchcraft" -- or, more often, some mutated specific strain of religious witchcraft.)
This leaves open the question of whether paganism in specific can be considered to have other obligations intrinsic to membership. My personal tendency is to judge the expected level of obligation against the level of effort required to gain membership in whatever community exists. If all it takes to get in to a community is to declare oneself a member, then it is positively insane to expect a significant level of obligation from other members of that community; the level of effort required to ethically maintain membership could become untenable with extreme rapidity. A very close or strongly committed community, with high levels of obligation and investment from members, will be much more difficult to qualify for -- consider the amount of effort it takes to form a family.
Of course, there will always be people who want to freeload; this is an inevitability when there are benefits to membership in a group. People will try to get those benefits without meeting their obligations; this leads to community policing efforts, either official or otherwise, or, in the longer and more unfortunate run, the fragmentation of the community. (This latter will tend to happen when people differ strongly in opinion about what members are responsible for.) That policing effort is reasonably construed as part of the obligation of community maintenance: the standards of obligation are in part what defines it, and someone who can gain benefits without meeting those standards will eventually bleed the community as a whole dry.
Which leads me to the question of burnout. In a large community primarily based on the low-cost entry barrier of declaring oneself a member, with very few explicit standards of responsibility, it is fairly easy to create energy drains with minimal repercussions. Since there is no agreement on standards of behaviour, things some people find objectionable within the community will be entirely acceptable to others, and this can produce repeated and somewhat messy arguments. Further, there will always be people who feel the impulse to care for and nurture their corner of the community more than, strictly speaking, they are required to: they will expend more energy than they can count on getting support back, simply as a matter of service (to themselves, to their community, to their gods). These people are a precious resource, but when there are drains in the areas that they have chosen to cultivate, they cannot continue doing so indefinitely. A support group can only go so far, and eventually many of these people retreat from the community entirely rather than continue to run themselves dry -- at least those parts of the community that are public, easily accessible, and the source of whatever it was that was causing them to get run down.
I see, sometimes, people suggesting that there should be more investment in the broad, easy-access community, that people have a responsibility or an obligation to care for it. The problem with this, from my mind, is that it means that other people can declare possession of my resources just by claiming an adjective, and those resources are already dedicated to my real communities, the ones I have extensive commitments to: family, ritual group, friends, and gods. I will give to other communities, but not because of obligation of membership, but for my own reasons and only with resources that are not already claimed.