Well said. "Cui bono?" is always the question, but cannot be answered at this point. I do not see any way that Russia might benefit from deliberately shooting down a civilian airliner. Ukraine might benefit if Russia could be blamed for it, as the new Kiev regime is shaky and desperately wants Western intervention. But I think the most likely explanation is that separatist rebels mistook this airliner for a Ukrainian Air Force transport (like the AN-24 they recently shot down) and took it out with a captured SA-17 system that they aren't fully familiar with. Eventually, we might learn what really happened.
The separatist shot down an AN_26 which has a service ceiling of 25,000 ft. The airliner was cruising at 33,000 ft. Why would the separatists shoot down an aircraft traveling thousands of feet higher than the supposed targeted AN_26?
I do not see any way how your analysis should begin with, "who benefits?"