  We present a theory for band-tuned metal-insulator transitions based on the
Kubo formalism. Such a transition exhibits scaling of the resistivity curves,
in the regime where $T\tau >1$ or $\mu \tau>1$, where $\tau$ is the scattering
time and $\mu$ the chemical potential. At the critical value of the chemical
potential, the resistivity diverges as a power law, $R_c \sim 1/T$.
Consequently, on the metallic side there is a regime with negative $dR/dT$,
which is often misinterpreted as insulating. We show that scaling and this
`fake insulator' regime is observed in a wide range of experimental systems. In
particular, we show that Mooij correlations in high-temperature metals with
negative $dR/dT$ can be quantitatively understood with our scaling theory in
the presence of $T$-linear scattering.
