Utilitarianism and Conscientiousness

While Kantianism and Mill's Utilitarianism are typically classified as rival Moral doctrines, two significant, interrelated, distinctions between them are that the Principle of the former is both unabashedly normative and integral to implementation, while the latter is insistently merely descriptive, having no influence on its object.  However, Mill's Principle is a response to Bentham's version, contesting, in particular, the thesis of the latter that the only consequences of one's actions that are relevant to the calculation of the Greatest Happiness are those to oneself.  In other words, his revised formulation, whether he acknowledges it or not, proposes a modification of selfish behavior just as much as does Kant's Principle, and, so, is no less prescriptive.  Thus, both that proposal and that modification are expressions of Conscientiousness--the proposal more conscientiously formulates Utilitarianism than does Bentham's version, while adherence to the modification more conscientiously promotes the Greatest Happiness than does selfish behavior.  So, though Mill might prefer to have his doctrine disassociated from Prescriptivism, he cannot as easily abstract it from his normative criticism of his Utilitarian predecessor.