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".

There is no author or legislator of the moral law. It is simply valid in itself in the nature or essence of things. We become autonomous only when we obey it, because then our will aligns itself with the objectively valid law, and our choice follows the same law as that we give ourselves. We can think of rational faculty (or the idea - the pure rational concept, not exhibitable in experience) as the legislator or author of the law because reason recognizes an objective standard, and to that extent is already aligned with objective moral truth.

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.

Clearly no working class movement ever came about that was able to do what Marx was hoping for.

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.

Marx is thought of as an implacable foe of capitalism. But go back and read the first section of the Communist Manifesto. Notice how it contains a paean of praise for the way capitalism and the bourgeoisie have both enriched the human powers of production and also enabled us to see with clear vision the nature of human society and human history.