On the whole how-can-CAM-blackmail-without-evidence thing, I suppose that should have bothered me more than it did. The fact that it did seem so plausible to me (and still does) seems like it points to a breakdown in my critical thinking skills - a bit not good for someone with yours as a philosophy grad student under her belt. :-)
For what it's worth, I think it helps to think of CAM's victims as falling into two basic categories: people who are afraid of scandal (with or without justification), and people CAM can hurt because of the information he holds, not necessarily proof. Lady Smallwood falls into the first camp. She's not concerned about what a fair reading of the facts would do to her, but what the mere whiff of the story, to people who see the headline and never read the details, what that would do to her family. It's the threat of an accusation, coupled with her own guilt or fear about the shamefulness of the situation, that make her vulnerable. And we've already seen one good man brought down by a story in the press that was true in some details and completely fictional in the ones that really mattered: Sherlock himself, in Reichenbach.
Group #2 are people who are vulnerable because of something he knows which they need to keep secret. Mary and John fall into this category. If you killed my sister eighteen months ago and were never caught, if I'm sick with grief over it I'm going to be highly suggestible. So if someone comes to me with a reasonably convincing story, with details that seem to make sense along with your home address, am I going to demand photographic evidence? Or am I going to confront you? All it takes is one overwrought grieving relative who could snap and go after John and Mary. And even if Sherlock and John are too strong to fall for CAM's machinations, Sherlock can't be sure that complete strangers will all be able to see through him. If you know enough details to make the story seem plausible, if you're good enough at manipulating folks, then CAM can still use other people against folks like John and Mary. Again, without necessarily having physical proof.
(Similarly, if CAM wanted to ruin Mary's life, all it takes is a well-placed phone call to the CIA or the MI6 saying: "I know where [AGRA] is, the assassin behind [still unsolved case]. She's living under the assumed name Mary Morstan Watson at [address], and if you'll compare her fingerprints to what you have in evidence, you'll see she's your woman." Again, he doesn't need proof that Mary did this; he needs to give just enough information to other people with access to that evidence, to connect the dots back to Mary.)
So I found it plausible that CAM could blackmail people with very little actual evidence. Particularly if he was coy about the fact that he had so little. He told Sherlock this because he was so sure he'd beaten Sherlock and this was Sherlock's final humiliation: that he'd been beaten by someone who could never have actually proven any of it. He simply gives Lady Smallwood the impression that he has those documents, and that seems to be his MO. I suspect the majority of people he blackmailed assumed he had actual proof on them. Mycroft probably assumed that, because it's what he would do. CAM's genius seems to be in realizing the danger of having actual proof, and also in how far he could go just form knowing what the proof actually was.
Btw, I was under the impression that while CAM didn't have proof on everyone, he did occasionally hold on to documents. Not necessarily at his home, and not necessarily in every case; but the simple fact that you don't know wht he can prove makes him that much more dangerous. If you don't know what documents related to which PTB in the British government would be found in the clean-up after an abduction or assassination, you can't very well go after him safely. In that regard, Magnussen's abduction would be potentially more dangerous to at least the upper echelons of British society than Moriarty's.
no subject
For what it's worth, I think it helps to think of CAM's victims as falling into two basic categories: people who are afraid of scandal (with or without justification), and people CAM can hurt because of the information he holds, not necessarily proof. Lady Smallwood falls into the first camp. She's not concerned about what a fair reading of the facts would do to her, but what the mere whiff of the story, to people who see the headline and never read the details, what that would do to her family. It's the threat of an accusation, coupled with her own guilt or fear about the shamefulness of the situation, that make her vulnerable. And we've already seen one good man brought down by a story in the press that was true in some details and completely fictional in the ones that really mattered: Sherlock himself, in Reichenbach.
Group #2 are people who are vulnerable because of something he knows which they need to keep secret. Mary and John fall into this category. If you killed my sister eighteen months ago and were never caught, if I'm sick with grief over it I'm going to be highly suggestible. So if someone comes to me with a reasonably convincing story, with details that seem to make sense along with your home address, am I going to demand photographic evidence? Or am I going to confront you? All it takes is one overwrought grieving relative who could snap and go after John and Mary. And even if Sherlock and John are too strong to fall for CAM's machinations, Sherlock can't be sure that complete strangers will all be able to see through him. If you know enough details to make the story seem plausible, if you're good enough at manipulating folks, then CAM can still use other people against folks like John and Mary. Again, without necessarily having physical proof.
(Similarly, if CAM wanted to ruin Mary's life, all it takes is a well-placed phone call to the CIA or the MI6 saying: "I know where [AGRA] is, the assassin behind [still unsolved case]. She's living under the assumed name Mary Morstan Watson at [address], and if you'll compare her fingerprints to what you have in evidence, you'll see she's your woman." Again, he doesn't need proof that Mary did this; he needs to give just enough information to other people with access to that evidence, to connect the dots back to Mary.)
So I found it plausible that CAM could blackmail people with very little actual evidence. Particularly if he was coy about the fact that he had so little. He told Sherlock this because he was so sure he'd beaten Sherlock and this was Sherlock's final humiliation: that he'd been beaten by someone who could never have actually proven any of it. He simply gives Lady Smallwood the impression that he has those documents, and that seems to be his MO. I suspect the majority of people he blackmailed assumed he had actual proof on them. Mycroft probably assumed that, because it's what he would do. CAM's genius seems to be in realizing the danger of having actual proof, and also in how far he could go just form knowing what the proof actually was.
Btw, I was under the impression that while CAM didn't have proof on everyone, he did occasionally hold on to documents. Not necessarily at his home, and not necessarily in every case; but the simple fact that you don't know wht he can prove makes him that much more dangerous. If you don't know what documents related to which PTB in the British government would be found in the clean-up after an abduction or assassination, you can't very well go after him safely. In that regard, Magnussen's abduction would be potentially more dangerous to at least the upper echelons of British society than Moriarty's.