  Astronomers have been using the measured luminosity to estimate the {\em
luminous mass} of stars, based on empirically established mass-to-light ratio
which seems to be only applicable to a special class of stars---the
main-sequence stars---with still considerable uncertainties. Another basic tool
to determine the mass of a system of stars or galaxies comes from the study of
their motion, as Newton demonstrated with his law of gravitation, which yields
the {\em gravitational mass}. Because the luminous mass can at best only
represent a portion of the gravitational mass, finding the luminous mass to be
different or less than the gravitational mass should not be surprising. Using
such an apparent discrepancy as a compelling evidence for the so-called dark
matter, which has been believed to possess mysterious nonbaryonic properties
and present a dominant amount in galaxies and the universe, seems to be too far
a stretch when seriously examining the facts and uncertainties in the
measurement techniques. In our opinion, a galaxy with star type distribution
varying from its center to edge may have a mass-to-light ratio varying
accordingly. With the thin-disk model computations based on measured rotation
curves, we found that most galaxies have a typical mass density profile that
peaks at the galactic center and decreases rapidly within $\sim 5%$ of the
cut-off radius, and then declines nearly exponentially toward the edge. The
predicted mass density in the Galactic disk is reasonably within the reported
range of that observed in interstellar medium. This leads us to believe that
ordinary baryonic matter can be sufficient for supporting the observed galactic
rotation curves; speculation of large amount of non-baryonic matter may be
based on an ill-conceived discrepancy between gravitational mass and luminous
mass which appears to be unjustified.
