If the Russians supplied the separatists with missiles, yes, I do think they should be blamed. We're talking about shooting down a Boeing 777, a passenger jet easily distinguishable from a military plane. You don't even have to possess military hardware to recognise it as a civilian aircraft. You do need some basic training to know what to do with the destructive power you've been provided with, however, but if the Russians did provide, I bet they skipped that particular lesson. There was no time.