Just as rule-consequentialists are more realistic if their cost/benefit analyses of codes count the cost of getting those codes internalised by new generations, they are more realistic if they assume that the internalisation will not extend to every last person. There will be some people who end up committed to mistaken views about what is morally allowed. Others will never have accepted any morality at all (psychopaths).  Rule-consequentialism needs to have rules for dealing with such people.