My own view is that Kant's conception of the duality of the good (morality and happiness, the good of our person and the good of our state or condition) is a distinctively modern view.
Kant has been famous for his rejection of eudaimonism, but I think Kantian ethics has a great deal in common with Aristotle, and some things in common with Stoicism as well. The traditions tend, I believe, to talk past each other when it comes to happiness or eudaimonia.
Kant can provide, and has provided, a good model for philosophers to think about the relation of metaphysics to science and scientific methodology.
Until I was a junior in high school, I was a "boy scientist" type and expected to go into chemistry. Then I discovered the humanities. I read the plays of Shakespeare voraciously, some novels, such as Pasternack's Dr. Zhivago and Sinclair Lewis' Main Street, and I got into philosophy by reading Kierkegaard and Nietzsche.
Smith could not be expected to have anticipated the horrors that were to come. But even in his own time, he was a defender of certain state actions that he thought necessary in order to safeguard the good effects of commercial society (Smith did not speak of 'capitalism' and was acquainted only with an early undeveloped form of it). Among these state actions the chief was general public education.
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.
Kant was a rational theologian. He did not pretend to be a biblical or revealed theologian.
Kant does not think there is anything wrong with being beneficent from sympathy. He thinks we have a duty to cultivate sympathetic feelings by participating in the situations of others and acquiring an understanding of them. He thinks we also have a duty to make ourselves into the kind of person for whom the recognition that something is our duty would be a sufficient incentive to do it (if no other incentives were available to us). That's what he means by "the duty to act from the motive of duty".
Kant does not think that along with choice of an action we also choose in each case the motive from which we do it. He thinks all is well if I act beneficently, realizing that it is my duty but also having sympathetic feelings for the person I help. But I ought to strive to be the sort of person who would still help even if these feelings were absent. And it is such a case that he presents when the sympathetic friend of humanity finds his sympathetic feelings overclouded by his own sorrows, and still acts beneficently from duty.
Notice that tearing oneself out of the insensible state is the opposite of remaining in it; the man who is beneficent from duty nevertheless acts with feelings, if not with empirical inclinations.
Kant does not regard freedom as an item of faith because it is too basic to our agency to be related to any end.
Freedom is an unprovable but unavoidable presupposition, not an article of faith.
We totally misunderstand both his aims and his contribution if we try to read into Marx some anticipation of either the modest successes or the disastrous failures of those who later thought they were acting in his name.
Clearly no working class movement ever came about that was able to do what Marx was hoping for.
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.
Marx's own illusion was to think that the working class movement, which he devoted his life to creating and strengthening, would both be socially and politically successful in the industrial nations of Western Europe, and that it would develop an entirely new way of human social life that would retain and even enhance the productive benefits of capitalism while overcoming the inhumanity and exploitation of capitalist social relations. Marx himself had no solutions to these problems. His object of study was capitalism itself.
It is absurd for anyone to think that Soviet "Marxism" is a correct application of the thought of Karl Marx. No doubt Soviet propaganda represented it this way. But who believes Soviet propaganda? It is remarkable (but maybe not so remarkable after all, when you consider their motives) that apologists for capitalism, who would not accept Soviet propaganda on any other point, are eager to agree with it on this point.
The Russian revolution did not occur until a generation after Marx's death. He was not involved with it, or with what came after it. His works do not describe post-capitalist society, and a fortiori they do not recommend any part of what the Soviet Union did.
There is a lot in Adam Smith that reflects the insights of Rousseau and anticipates those of Marx.
There is a tradition of "modernist" theology arising out of post-Kantian thought - Fichte was the real father of it, but Schleiermacher and others also developed it - which might have more promise if it had greater influence on popular religion.
I think the contribution people make is not proportionate to their fame or success. In fact, I think the relation is often inverse.
