I don't think Kant's theory looks bad to people except insofar as they have misunderstood it (for instance, as heartless and ironheaded, or as committed to an absurd metaphysical conception of freedom that violates Kant's own philosophy).

Kant was a rational theologian. He did not pretend to be a biblical or revealed theologian.

One rational standard of action is how well it promotes the end it seeks. Another standard is whether it aims at ends which are good. Both of these, but especially the former, depend on judgments of fact.

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.

Being aware of truths about what is good or right or about what we ought to do is not the same as deciding what to do. Nor can the former truths be derived from decisions about what to do, or about procedures for making such decisions, unless these procedures themselves rest in some way on the apprehension of truths about what we ought to do.

In my view, there was a long period in which analytical philosophy had little to say about ethics. I think their intellectual tools did not do well with it, and analytical philosophy was above all about revolutionizing the philosophical tool box. It was more or less assumed that the Truth about ethics was some form of utilitarianism (perhaps because some consequentialist calculus looked to them like a respectable tool). Kantian ethics was then interpreted as a particularly odious version of the False - "deontology" - and treated with contempt.

The problem is that many who reject Marx do not read him, or read him only by bringing prejudices to their reading that prevent them from understanding him.