I think that one should be grounded in real life physics.
All experiments have measurement errors and all experiments measuring quantum states have measurement errors. These may come from the instruments but they may also be effective measurement errors because of the enormous order of magnitude differences within the various measures of the quantum states.
For example in simple potential problems gravity should be taken into account in solving Schrodinger's equation, but the difference in the effect between an electric potential and the gravitational potential allows us, within our measurement capabilities to ignore g and get correct verifiable results.
Decoherence is best seen in the matrix format where the overlap of the pure states fills the off diagonal elements of the density matrix. In a completely decohered state there would only be density matrix elements on the diagonal, the expectation value of each pure state, that can build up the classical view.
Now suppose ( a hypothesis) the universe could really be described by such a density matrix completely, all the elements of the matrix filled with accuracy. There will be enormous order of magnitude differences , making practically all non diagonal elements within errors zero with respect to the diagonal ones. On the one hand the small gravitational constant, on the other the distances between matter conglomerates, on a third the small value of h ( the Planck constant) all will guarantee that decoherence is a measurable reality, except for localized clusters within the accuracies of h .