 Contractualist reasons are more flexible than aggregation, as they allow us to respond directly to morally relevant considerations, rather than having to rely upon some complex utilitarian calculation. (Think of the artificial epicycles a utilitarian needs to go through to reject a principle that efficiently maximises happiness, but happens to be racist or arbitrary.) By moving straight to the moral heart of the matter, contractualism also seems to offer a more satisfying explanation of why certain behaviour is wrong.