It is plausible (though not necessarily true) that refusing to be blackmailed acausally prevents the AI from becoming a torture AI, but it cannot prevent the AI from existing at all. How could it?
In this case "be blackmailed" means "contribute to creating the damn AI". That's the entire point. If enough people do contribute to creating it then those that did not contribute get punished. The (hypothetical) AI is acausally creating itself by punishing those that don't contribute to creating it. If nobody does then nobody gets punished.
In this case "be blackmailed" means "contribute to creating the damn AI".
To quote someone else here: "Well, in the original formulation, Roko's Basilisk is an FAI that decided the good from bringing an FAI into the world a few days earlier (saving ~150,000 lives per day earlier it gets here)". The AI acausally blackmails people into building it sooner, not into building it at all. So failing to give into the blackmail results in the AI still being built but later and it is capable of punishing people.
Todays xkcd
I guess there'll be a fair bit of traffic coming from people looking it up?