What was Putin's annexation of Crimea then? Is not Russian policy in Syria equally batshit insane?
Russia is supporting the sovereign Syrian state against foreign proxy mercenary forces. You can't really argue against this; however you may feel about Assad, he is the sovereign leader of Syria and Syria is a sovereign state. What Britain and the US is doing in Syria is actually contravening the sovereignty of another sovereign state without the reason of direct threat to their own territory (this is why Blair tried to argue for the 40 min WMD; he needed the threat to his own territory to make the argument for the invasion of Iraq to the UN security council). This essentially makes the British Syrian action an invasion, and against any understanding of international norms. This is what Putin is trying to say.
You fuck with these understandings, and you've got a serious geostrategic problem.
A similar scenario would be the Chinese deciding to bomb Britain because they decided they didn't like Teresa May and wanted to support the upswell of a "revolutionary" movement that essentially consisted of a bunch of non-Brits who'd been enticed to come to Britain to fight for shit and giggles.
Crimea is complicated. The EU knew that they were asking for trouble by challenging the politics around a Black Sea port that led to the Bosphorus and through into the wider Med, but they did it anyway.
A lot of this goes back years, particularly under the previous Labour government that didn't notice the power they had given the Russian state by not challenging the "awkwardness" of Gasprom contracts that delivered energy throughout Europe (at one point, Russian gas was fueling a number of NHS hospitals and York Minster). Now everyone has noticed and they are panicking and making stupid, panicked decisions. Syria is one of them. It stands in the way of a pipeline from Qatar to Europe, designed to dissolve European dependence on Russian gas.
We are the bad guys here. And I really wish people would see it.
Putin, I have to say, is being very measured. And I am no fan of the Russian administration.