The easiest answer: who is their target? By knowing the target you know the attacker. I have some clues, do you? 
That question does not make sense as it is labeled in the title "bring down Bitcoin". Bitcoin has a decentralized flow of money, it brings that power back to the people where it belongs.
This is a threat to the economic elite. At first they did not recognize that threat, but now that it is clear Bitcoin is real, they recognize the threat is real. They can't take it down directly, but what they can do is attempt to seize control of the network. And that is what I believe they are trying to do, using the very social engineering tactics quoted in your original post.
The worst part of this is that genuine people are being manipulated by the campaign and they're indirectly joining it. This does make a lot of sense if you consider:This is a threat to the economic elite. At first they did not recognize that threat, but now that it is clear Bitcoin is real, they recognize the threat is real. They can't take it down directly, but what they can do is attempt to seize control of the network. And that is what I believe they are trying to do, using the very social engineering tactics quoted in your original post.
1) Bitcoin "has many enemies".
2) Bitcoin can't be damaged otherwise (no known exploits).
3) Humans are flawed.