The chaos in Syria should be blamed on Assad's repression and brutality from the start of the uprising against him. But it has been 4 years. Solutions that were possible then are not possible now.
I would argue that there is no possibility of a peaceful democratic united Syria at the present time. The only question is which brutal dictatorship will win in the end, how long it will take, and where else the conflict will spread before it is done.
In this environment, supporting Assad may end up being the least bad option for both Syrians and the region. Efforts to create a pro western rebel group have largely failed. The non-ISIS rebels are almost entirely also Islamist. Their victory will lead not only to repression of non-fundamentalists but also to massacres of minority groups such as the Alawites.
Putin has certainly capitalized on western inaction to enter the conflict, but the West was not acting because there are no good options. If Russia stays in, this intervention has a high potential of becoming another Afghanistan for Putin. It is most likely yet another long-term loss masquerading as a short term win.
My preference is to let Putin try. Either he will improve a hopeless situation or he will weaken his own regime in the process of failing in Syria.