You are indeed correct that it simply floating would do nothing. However, if you spin it, it will act as though it was in a vacuum causing it to spin indefinitely as it acts differently to a floating plate. The field generated by the cat-butter is based off of two different laws trying to achieve the same true value. If it were to obtain equilibrium, that would mean a bias towards one of the particular laws either the bread, or the cat.
Ah, but are the cat-force and butter-force separate forces, or manifestations of the same natural phenomenon?*
You would be well advised to not think of "laws" of physics as synonymous to forces of nature. They are merely our descriptions of the nature.
Also, multiple forces can reach an equilibrium quite fine, otherwise matter would not exist in stable configuration. Repulsing and attracting Coulomb forces, strong nuclear force, gravity, inertia... equilibriums exist everywhere in the nature, and just as abundantly there is a presence of naturally oscillating systems that demonstrate a fine byplay of energy exchanges through the forces of nature.
*Superficially both would seem to be related to gravity, but in deeper inspection gravity proves to only be the defining force for direction of general movement (gravitational acceleration). In case of bread-butter force, the main phenomenon would be possibly air resistance providing stabilizing tendency to settle on a butter-first flight state, and the tendency of human mind to statistically favour negative events in perceptive memorization. Cat-force is mainly just cat's remarkable skill in controlling its position while falling, utilizing its limbs, tail, and body to flail around to achieve desired attitude before impact.
Yes. I just suggested that both cat-force and bread-butter-force are apparent forces rather than real forces.
Just like gravity, coriolis-force, and centrifugal force... their existence depends on choice of some very specific reference frame (of mind). If we exit such reference frame, said forces disappear...
