Kant's aim was to develop a religion within the boundaries of mere reason (that is, reason unaided by special empirical revelation) and then to ask about existing ecclesiastical faith (especially about Christianity, and the Lutheran Christianity of his time and place) how this revealed faith must be interpreted if it is to be reconciled with reason, and even seen as a wider (though morally optional) extension of a religion of reason.

I think that both Mill and Sidgwick are great and admirable philosophers, from whom we still have a lot to learn. I would not favor a form of Kantianism (if there is such a form) that treats Mill's or Sidgwick's moral philosophy with disrespect.

If we decide rightly what to do, or use a correct procedure for making such decisions, that has to be because the decisions or the procedure rest on good reasons, and these reasons consist in the apprehension of truths about what we ought to do. Because these truths must constitute reasons for our decisions, and because in the rational order, reasons must always precede the decisions based on them, the truth conditions of claims about what we ought to cannot be reduced to, or constructed out of, decisions about what to do, or procedures for making such decisions.

We commit not only theoretical error but also moral wrong in objectifying ourselves or other rational beings, ignoring their capacities for free action and communicative interaction with us.

Descartes recommended that we distrust the senses and rely on the ... use of our intellect.

Popular religion since the time of Kant and Fichte has gone in a direction they tried to prevent and that has been disastrous for the humanity both of believers and of the rest of us. Look at the role of religion in Republican presidential primaries if you need any confirmation of this last statement.

What Smith and Marx have in common is that they were both philosophers of great vision and perceptiveness, deep humanity, and a sense of social reality that has been lost in the abstractly formalistic economic theories that have dominated the field since the last third of the nineteenth century.