  The bulk viscosity of two-component fermions with a zero-range interaction is
revisited both in two and three dimensions. We first point out that the
"standard" Kubo formula employed in recent studies has flaws to give rise to an
unphysical divergent bulk viscosity even in a limit where it is supposed to
vanish. The corrected Kubo formula as well as the sum rule is then carefully
rederived so as to confirm that the bulk viscosity indeed vanishes in the free,
unitarity, and dimer limits. We also discuss that the recently found
discrepancy between the Kubo formalism and the kinetic theory for the bulk
viscosity is attributed to the fact that the quasiparticle approximation
assumed by the latter breaks down even in the high-temperature limit.
