  We comment on what the naturalness argument of 't Hooft implies for a minimal
extension of the standard model which incorporates right-handed neutrinos with
generic mass terms. If this Lagrangian is taken as a low energy effective
theory, the idea of pseudo-Dirac neutrinos with very small masses is consistent
with the naturalness argument of 't Hooft. This argument is based on an
observation that the right-handed components of neutrinos in the massless limit
exhibit an extra enhanced symmetry which is absent in other charged fermions.
This enhanced symmetry is reminiscent of the Nambu-Goldstone fermions
associated with spontaneously broken supersymmetry. The conventional seesaw
scenario gives another natural solution if the ultra-heavy right-handed
neutrinos are integrated out in defining a low energy effective theory.
