Nothing can exist in a vacuum, and it does not contribute anything to the community to isolate itself utterly from society at large, this would only generate suspicion and resentment between the two groups, those creating an us and them mentality. The community should make as much as possible available to the public; libraries, videos of lectures, personal blogs, transcripts of of dialogues, finances, taxes it should be clear there is nothing to hide about the community.
The second major reason, is income, the members will be paid in savings, due to the spread of costs cheap-shared labour, and food. The income to the community should be reasonably, higher than the outgoings and costs. A large proportion of the excess money should go into savings for future difficulties and growing new communities.
The final benefit of engaging with a variety of different groups is a growth of understanding their requirements and through our work, research and testing; improve charities, foundations and opensource technologies and through those efforts help the world and the next generation. However, no work should be done that be done that goes against the ethics of the community.