It is often difficult to know about one's own era which philosophers in it will be remembered as the most important ones, but I think it is already clear that John Rawls is the greatest moral philosopher of the twentieth century.
I think the term "Kantian constructivism" as an oxymoron. Kant was a constructivist about mathematics, but not about ethics.
It is probably not a good idea to ask someone to expound a position they do not accept and do not feel they even fully understand.
For the utilitarian, there is a fact of the matter about the good (the general happiness, or whatever conception of the good the utilitarian adopts) and about which actions or moral rules would contribute to maximizing the good. For the rational intuitionist, there are truths about which actions should be done and not done.
Being aware of truths about what is good or right or about what we ought to do is not the same as deciding what to do. Nor can the former truths be derived from decisions about what to do, or about procedures for making such decisions, unless these procedures themselves rest in some way on the apprehension of truths about what we ought to do.
Our decisions need not be seen as resting on procedures that are merely instrumental in making judgments that are reliably truth-tracking. The procedures might be more directly related than that to truths about what is right or good, or about what we ought to do, or to principles that tell us what is true about these matters. And I have no metaphysical theory about the truth-conditions of such truths, except to say that as objective truths, they must be independent of the attitudes, decisions or actions that they are supposed to justify or for which they are to offer reasons.
I think it is clear that what we ought to do has to be independent of our decisions about what to do, and independent of any procedures we might use in making such decisions.
In any matter of moral importance, our first task, before we plunge ahead and decide what to do, is to figure out what we ought to do.
We can make mistakes about what we ought to do, and these are not the same as making bad decisions about what to do.
I think if there were to be a solution to the problem of free will, it would have to be a compatibilist one. Unfortunately, from that it does not follow that there is such a solution. Many philosophers find this an unwelcome message, and as often happens in philosophy, they punish the messenger by ascribing to him an entirely imaginary but untenable position.
Kant does not think that the silly commandment "universalize your maxims" is the be-all and end-all of ethics or that it provides us with some sort of general decision procedure that is supposed to tell us what to do under all circumstances.
The problem I see with utilitarianism, or any form of consequentialism, is not that it gets the wrong answers to moral questions. I think just about any moral theory, worked out intelligently, and applied with good judgment, would get just about the same results as any other.
I don't think Kant's approach to religion is any longer viable in its original form. But that does not mean it is simply wrong or that we cannot learn from it.
Kant attempted to work out a view of religion and religious belief according to which existing religions could be brought into harmony with modernity, science and reason.
Many who are committed to reason and science have turned against religion altogether and treat it with fear and contempt.
Sometimes when a philosopher's views are widely rejected by the world, the fault is not with the philosopher but with the world.
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.
Kant did think he had a moral route back to rational faith in God, for those who need it, and he thought that at some level, we all do need something like it.
Utilitarians are usually empiricists who think they can solve every problem by accumulating enough empirical facts. They do not realize that thinking as well as experience is necessary to know anything or get anything right.
It was an important part of Mendelssohn's philosophical and religious view that the traditional rationalist proofs for God's existence should be sound an convincing. Kant thought they were not. So Kant's critique was world-shaking for Mendelssohn.
One rational standard of action is how well it promotes the end it seeks. Another standard is whether it aims at ends which are good. Both of these, but especially the former, depend on judgments of fact.
Philosophy is about getting the facts right, but it is also about thinking rightly about them. Philosophy is more about the latter than the former.
Kant thinks we can show that there is no contradiction in supposing we are free.
We can establish empirical criteria for free actions, and investigate human actions on the presupposition we are free.
We can treat human responses to cognitions as involving law-like connections grounded on free choices which show themselves in our character.
