Quite the premises. Even dualists and others who might support this view would certainly not be content to treat them as undefended assumptions.
You have assumed there is an external universe. The only access we have to this universe (assuming it exists) is via physical interactions with it (seeing, touching, etc.), and inferences from such interactions combined with internal conceptual frameworks, the mind, etc. Thus, for example, in cosmology one regularly finds physical descriptions of phenomena which have never (and in some cases can never) be observed in any sense other than by applying thought to the mathematical structures in physical theories. Physical "laws" are formed by generalizing the results of experiments and observations to form abstract descriptions. They are not external (which is why they have either all proven to be wrong, or to force us to realize that we cannot be treated as pure "observers", isolated from the cosmos we both seek to describe and participate in).
Also, and more simply, there exists no set of physical laws that can be said to describe everything we hold to be physical, even under the assumption that everything can be said to be physical in the sense used in modern physics and reducible to interactions among the most elementary components we can speak of (which depends upon the mathematical framework, problem, and scale concerned; composite particles can be and are taken to be elementary in theories which treat would-be more "elementary" fermions as the building blocks as topological features of the truly elementary bosons).
By this kind of argument, software and programs more generally aren't physical, because they are also things we treat in the abstract, ignoring their physical realizations.
Why eternal? Why can't these assumed laws, for which we have no evidence, evolve?
You make many great points that help explain why I'm moving away from dualism now too.