Russia has murdered dissidents multiple times in foreign capitals in plain view (resulting in other civilian deaths) most recently the Novichok murders. They don't care about what the west thinks and likely approved this operation too.
That's not true actually. Not a fan of the modern Russia but a fan of accuracy. That plane was shot down by rebel Donbass forces by mistake. They were not well trained and mistook it for a military plane.
Good question. Who knows, all I know is that it is time to really de-escalate relations between the big power blocks. At the same time Western democracies have to put limits on what totalitarian regimes, true and wannabe ones, are allowed to get away with. These things seem to be mutually exclusive so. I always thought the Putin is the most dangerous and cunning leader the world currently has. I also thought that this cunning would prevent him from doing anything stupid. Not so sure anymore about the last bit anymore, given with what he got away with so far.
Don't ask me what Western powers should do so. Given the loss in soft power in the last decade, throwing out human rights by the EU during the refugee crisis and ever since, the new alliance between Israel and Saudi Arabia, Trumps foreign policy, options seem to be limited.
Nobody is going to ban Russia. Look at the map. How do you think they'd fly between EU and China/Japan? Over Russian territory. Case closed, even not talking about nukes and stuff, just on economic reasons. For heaven's sake, they are finishing a major gas pipeline between Russia and Germany (look up North Stream 2), what bans could there be? Russia is not Belarus (even though Belarus is definitely a puppet of Russia) and EU would not dare to go as far, however nice it would sound. And Putin knows that very well.