That is an amazing video, lonelyplanetmum I LOVE the antidotes (engagement! vote like your life depends on it!) that they propose.
I'll bet this isn't answering your question, lonelyplanetmum. I'll bet I'm not going to say anything you don't already know.
But I'm going to have a go - just to encourage other, wiser, people than me to step in. Because it's a great question. And i've realised that a lot of people don't know that much about modern Russia.
Well, part of it is asymmetric warfare. If you imagine international relations to be a kind of state of anarchy, with lots of nations struggling to maintain and extend their position, how does a nation with a relatively small GDP (Russia has a relatively small GDP) maintain or even extend its position, integrity and existence against other, larger nations?
One way is by building alliances - and here, you need to have interests you can share, trade, etc. Generally, nations opt for stability and relations. Another thing you can do is actually go to war, in the old sense of war - very risky, especially if you are relatively poor and also war carries all sorts of risks in the modern world - not least because there are lots of relationships governing international relations, so an act of aggression has consequences beyond any immediate act of aggression.
Asymmetric warfare covers acts of aggression that are waged by relatively powerless nations against others - such as 'terrorism', and forms of warfare that fly below the radar of what counts as war in the old sense of the term.
That, in part, explains why Russian aggression (the troll farms, etc.) takes the form it does - but doesn't explain the why.
The 'why' is more complicated. Partly, it's because that poisoning of social media - and mainstream media within Russia - has been going on a long time within Russia itself. So it's a pre-existing format. The poisoning of media has been incredibly effective within Russia. As people keep saying, Russia is a very corrupt kleptocracy. How do you get a population to go along with a corrupt kelptocracy? Well, one way is to create the idea of a 'state under threat', and the idea that people have to rally around 'the nation's interests' in the face of an enemy.
There's been a fair bit of that in Russia, war with Chechnya for example. But very effective has been the silencing of an oppositional media.
One way Russia has silenced an oppositional media has been brutal: state control and actual deaths of journalists. Another way has been to simply poison social media: filling it with fake news, propaganda, trolls, whatever - and making it just such a crap, confusing, vile place that nobody can actually effectively use it.
If people can't effectively communicate, it becomes very hard to develop ideas about opposition, develop strategies for opposition and dissent, and just organise. without an effective opposition, it's so much easier to govern people. And people are human - if you have people who are just depresses, switched off from participation in politics, who actually believe there is just no point, or are utterly cynical to the point of non-participation - then you have won an incredibly important victory for the status quo.
So, in part, all of this is the exportation of strategies that have been used in Russia - and in expat communities and in areas like Ukraine - for a long time.
But it is also an aspect of Russia's foreign policy, too. I have to apologise here, because there are actual names for some of these programmes, and I can't remember them. 
Part of Russia's foreign policy goes back to that basic idea about how a nation with a small GDP can thrive in the free for all of international relations. One way is to build relations. There are slight problems here.
International relations with powers like the US might come with strings:
a demand by the US to be allowed to buy gas at a cheap price, or to be able to invest in Russia, or (sometimes) the demand that Russia follow rules about human rights internally, and follow a particular foreign policy outside its borders (eg. no invading places).
This is a bit tricky for Russia: maybe they went to sell natural resources at a higher price, maybe they don't want to follow the US model on humna rights, maybe they don't want to follow the foreign policy demands, maybe - and this one is quite crucial - they don't want to follow the investment protocols (the kleptocracy likes to keep control of the money and foreign investors don't like suddenly having all their investments vanish and discovering 'the rule of civil law' is pretty shaky).
So a foreign policy based on relationships has complications.
There is a also an idea that it has to be proved that Russia is something other - better - than liberal democracy. That message is important for its domestic policy but it has implications for its international dealings.
The upshot is that Russia seems to have opted for a tactic of destabilising other nations.
If other nations are a bit knoecked off balance, it proves the idea that western liberal democracy is a flawed programme and is in imminent danger of collapse (you'll notice, here, the direct similarity with a lot of the Leave rhetoric which bangs on about the EU being a flawed project, in imminent danger of collapse).
This shores up the internal message to the domestic population of Russia (Hey folks, Russia is great, there's no alternative. Get back to work.) as well as sucking energy from the other nation, making them less likely to pursue foreign adventures of their own. If everything's going bonkers in your country, you have less opportunity to worry about, or attend to, the sphere of international relations.
There is also a very strong message from Russia - directed towards its internal electorate but also perhaps governing its international relations - that Russia is a power that is unfairly excluded from a global hegemony. Globalisation is a terrible force, a cabal essentially, that acts against Russia, is morally wrong in that it punishes small nations and strangles native expression, and is inherently unstable. It is part and parcel of the stranglehold Western liberal democracy holds on the world.
You'll recognise this one from the Referendum, too. And from people like George Galloway
So Russia is morally superior in supporting nativist, often right-wing, movements that are trying to assert themselves authentically against this hegemony.
Of course, it's result is to destabilise pre-exisiting global relatinships and to weaken structures - such as the EU and even the US - which currently exclude Russia, or have limitied relationships with Russia. And I guess the hope is that, when those relationships are re-organised and re-established, the deals made and the relatinships formed with Russia, will be on better terms.
There's an actual, proper name for this policy. And i can't remember it. I think it starts with 'p'. 
But why go for troll farms and making social media so horrible?
Well, that's divide and rule. A nation that has problems domestically is far less likely to pursue an aggressive foreign policy - whether that foreign policy is one of expansion or simply maintaining it existing relationships in a firm way. Still less is it going to take on the role of 'world policeman', monitoring relations beyond its own interests.
What has been fascinating about the whole Russian thing is how effective it appears to have been - though that is really up to historians of tomorrow to assess. Who would have guessed that social media really was a platform by which you could attack the fabric of another nation? And who would have guessed that going for cynicism, getting people to switch off from the democratic process, etc, could be so effective?
Well, you could say that a nation that has found that effective internally might have guessed. But, actually, I don't think anyone actually did.
Obviously, having a destabilised nation is effective. Breaking up a rival economic power, such as the EU, or even just destabilising it, has an obvious advantage. Destabilising a major power, especially one that is known to take an active role in international relations, and getting it to turn its attention towards domestic matters, has an obvious advantage.
Actually managing to install a President who is very friendly towards your nation's interests - whether that is by being happy to allow you to maintain the (corrupt civil law) internal status quo in your nation, refusing to impose agreed sanctions, brokering new, favourable deals, turning a blind eye to your foreign policy ambitions (even if that means existing international relatinships are going to be serioiusly re-ordered) - is a massive victory. Really amazing.