The relation of the law to the self is only a helpful way of thinking about the law, that helps us better understand its validity for us.

Kant thinks that a free will is a will under moral laws and that freedom and the moral law are distinct thoughts that reciprocally imply each other. Fichte thinks they are the same thought.

We can make mistakes about what we ought to do, and these are not the same as making bad decisions about what to do.

We cannot predict the effects of our actions, especially our collective actions over generations or centuries, to use instrumental reasoning toward these big final ends to tell us what we ought to do.

Capitalism now seems more likely a swamp, a bog, a quicksand in which humanity is presently flailing about, unable to extricate itself, perhaps doomed to perish within a few generations from the long term effects of the technology which seemed to Marx its greatest gift to humanity.

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.

It would be nice, wouldn't it? if we could get comfortable about the problem of freedom. Kant thinks that we can't.