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.

In fact people do not know enough about themselves and what is good for them to form a sufficiently definite conception of the general happiness (or whatever the end is) to establish definite rules for its pursuit.

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.

It seems to me self-evident that it is worthwhile to understand the best thoughts of the past, to appropriate them, to criticize them.

When people think that moral problems can be solved by some simple strategy of calculation, that sets them up for ghastly overreaching. They think they can turn everything into a "science" the way mechanics was turned into a science in the seventeeth century. They want to turn everything over to technocrats and social engineers. They become shortsighted or simplistic about their ends, and they disastrously overestimate their ability to acquire the information they need to make the needed calculations.

I think the contribution people make is not proportionate to their fame or success. In fact, I think the relation is often inverse.

As with many metaphysical and religious questions, Kant thinks they lie beyond our power to answer them. If you can't stand the frustration involved in accepting this, and insist on finding some more stable position which affords you peace of mind and intellectual self-complacency, then you will find Kant's position "problematic" in the sense that you can't bring yourself to accept it. You may try to kid yourself into accepting either some naturalistic deflationary answer to the problem or some dishonest supernaturalist answer.