[andrewflnr]

My point is that "should" is redundant with "want" in a materialist viewpoint. It only makes sense to talk about "should" separately from desire if they're not necessarily the same. Is this not tautological? You need some other set of axioms describing some goal other than want-satisfaction and an assertion that it's true for everyone before you can meaningfully call it "morality", a system containing "should". Otherwise it is, as you put it, an ungrounded symbol.

In other words, a moral system needs to answer the question "why should I give a #$@*?". Why not let the world burn if i feel like it? Why not just that part over there that's only being used by people I don't like and don't depend on? Your Kant quote is a succinct statement of the commands of most moral systems, but doesn't answer the real question. If there's nothing more to the universe then we can see, only matter in odd configurations, I don't see how it can be answered.

P.S. I'm not sure what you meant by "real desires", but it bears mentioning that there exist people and other beings whose real desires are purely destructive, to others and themselves; self interest in the usual sense (survival and comfort) is not necessarily relevant. Think about people we class as "mentally ill" (which really just means outlier, since our "healthy" baseline is just the average). If you didn't mean to imply that no one has a "real desire" in some sense to do "evil" things like destroy all life on earth, then you can probably ignore this part, but it had to be said