I don't believe blackmail is the most effective thing. The problem with blackmail is that even if you do as the blackmailer says, they still have the threat hanging over you forever. That increases the risk that they do something desperate.

What is effective, isn't blackmail, but complicity. Doing bad things together. Then you get a shared interest. The people Epstein had blackmail on, knew that he wouldn't use it casually, because after all there would be no way to use it without implicating himself. But if he were desperate, he might. So the victims had an interest in keeping Epstein not desperate.

So it's the bad things they do together which is dangerous. Even things they do in full view of the public can work, because the threat isn't necessarily that the public finds out, it's that if one is held accountable, then all are at risk.