Full Idea
A particular weakness of the contractual theory is that it is unstable with respect to a superior agent, one more intelligent and resourceful and persuasive than the rest.
Clarification
'Contractual' theories see morality as mutual back-scratching
Gist of Idea
A weakness of contractual theories is the position of a person of superior ability and power
Source
Bernard Williams (Ethics and the Limits of Philosophy [1985], Ch. 3)
Book Reference
Williams,Bernard: 'Ethics and the Limits of Philosophy' [Fontana 1985], p.31
A Reaction
The very weak are equally a problem. Democratic societies produce fewer inequalities. Hierarchical societies are miserable (I expect..).