Reasonable persons ... desire for its own sake a social world in which they, as free and equal, can cooperate with others on terms all can accept. They insist that reciprocity should hold within that world so that each benefits along with others. By contrast, people are unreason¬able in the same basic aspect when they plan to engage in cooperative schemes but are unwilling to honour, or even to propose, except as a necessary public pretense, any general principles or standards for speci¬fying fair terms of cooperation. They are ready to violate such terms as suits their interests when circumstances allow.