I think that there might be another sociological factor enabling the Russians in this adventure and, probably, discouraging domestic dissent: racism.

Russians, and muscovites in particular, have a lot of disdain for the peoples of the Caucasus. The common slur is “chernozhob,” which translates as “black ass.” Although Georgians and Armenians, as christians, occupy a slighter higher social niche than Chechens or Azeris, they are viewed as inferior to Great Russians. Georgians, and other Caucasus peoples, are considered to be prone to criminality, dishonest and dirty. The Moscow authorities routinely round them up and expel them from the Russian capital. Russians do not think of Georgians as “European.”

I think that one reason that Russians support the military operations is Georgia is this disdain for “those people.”

I also think that one reason the Russians are allowing the S. Ossetian militia and various *volunteers* to operate freely in the areas of Georgia that they control is because Russian public opinion has a certain comfort level with the thought of different chernozhopy fighting each other. That is what “those people” do, after all.
The Russian army has plausible deniability, they are not themselves involved in the ethnic cleansing, and it is so hard to control these excitable people.