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.

Karl Marx left it to others to find the way beyond capitalism to a higher form of society. He saw his role as giving them as accurate a theory as he could of how capitalism works, which would also show them the reasons why it needs to be abolished and replaced by a freer and more human form of society.

As I understand it, Kantian constructivism is partly a position in normative ethics and partly a position in metaethics. In metaethics, it is the position that ethical claims have truth values, but their truth conditions consist not in a set of objective facts to which they correspond, but instead in the outcome of some procedure of deliberation resulting in decisions about what to do.

Kant was a rational theologian. He did not pretend to be a biblical or revealed theologian.

Kant can provide, and has provided, a good model for philosophers to think about the relation of metaphysics to science and scientific methodology.

There is a lot in Adam Smith that reflects the insights of Rousseau and anticipates those of Marx.

Kant does represents a distinctively modern view of the human condition in contrast to that of ancient high culture, found in ancient Greek ethics and also in ancient Chinese ethics.