The term "society agreement" refers to the rights and obligations that an individual has in a society: wanting certain rights brings certain obligations. My island model explains how these two connect if one wants to optimize the society toward greatest benefit and least obligations:
Each thing produced in a group is produced by certain inidviduals or groups: for example food by farmers and cooks plus transported and sold in shops. Let's group all these persons to an island.
The society agreement says: If you want some benefit, support the slands that create the benefit. For example safety (moral & police), exchange (moral, trustworthiness, trade and money), hobby groups and federations which support certain cause, etc. If you do not support an island, you are not allowed to gain the enefits that that island produces except via exchange. You can support a general cause like all ok hobbies. This view point in use in a society can make different parties and organizations an expression of the major current of the life in the society and so support the freedom of opinion a lot, and of course support moral freedom at large a lot. All groups fit together via justice as a practise in the society, as a practise supported by the people in that society at large, by the general opinion and by the individual deeds f all who get to know about those things - this is so because their best understanding, heart and mind together and their moral, learned wisdom, the words of the wise, and their likings WITH a picture of the whole in thinking etc. support such course of action. In addition responsibility, common sense like thinking with a pictrure of the whole, and the rule "Live and let others live!" support success in such arrangements. See http://Finnishskills.blogspot.fi
When one sees all islands in a society, one can see all the things that that society produces and say who is allowed those benefits. In addition one needs such picture of the whole world.
This way one can optimize a society morally ok. On each island the benefits and obligations are shared according to justice.