What I most fear now is that within a century or so there may not be any human future at all.

Kant regards the universalizability test for maxims as focused on a very special sort of situation: one where the agent is tempted to make an exception to a recognized duty out of self-preference. The universalizability test is supposed help the agent to see, in a particular case of moral judgment, that self-preference is not a satisfactory reason for exempting yourself from a duty you recognize. Kant thinks, as a matter of human nature, that this situation arises often enough and that we need a canon of judgment to guard against it.

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".

When Marx, in the Theses on Feuerbach, says that only idealism up to now has understood the active side of material Praxis, what he says is more true of Fichte than of any other philosopher in the classical German tradition.

We usually can't know how, and we probably should not even ask, how our lives contribute to a better world.

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.

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.