No purity spiral every spirals towards truth.

Purely hypothetically, lets pretend the world was taken over by extremely corrupt and evil people, who took hold of the positions of power, a hundred or so years ago. Then, they start exerting greater and greater influence upon all the institutions of society, as they further infiltrate and subvert those institutions, using them to put forth propaganda and lies to brainwash people. The institutions become so corrupt that they now push forth only lies and propaganda, which were able to brainwash entire generations because of their monopoly of control over all mediums of information sharing. Let's also say, purely hypothetically, that a new medium for information sharing is invented (we could call it "the internet"), which lets average people talk to each other outside the confines, control, and censorship of the mainstream media. This new medium allows people to discuss the truth, to spread the truth, person to person. Over time, this discussion of truth wakes more and more people up, not just to the overt lies, but to the small ones, and to the big ones that have been fully ingrained into all of society by this point.

In this purely hypothetical scenario, the brainwashed masses, merely by discussing and spreading the truth, will ipso facto participate in a purity spiral towards truth, because the only things they're disproving and getting rid of are lies and propaganda, as they move back toward the truth, the truths which were abandoned and censored previously as the evil people in power began to exert control over information sharing.

This doesn't necessarily mean that all the posited alternatives are true, but it does mean that the outright lies are being rejected, which necessarily will mean that, purely from a numbers game, more truth will be embraced than not, comparative to the possibility that the people had remained under the control of the propaganda and lies.

No purity spiral every spirals towards truth.

Purely hypothetically, lets pretend the world was taken over by extremely corrupt and evil people, who took hold of the positions of power, a hundred or so years ago. Then, they start exerting greater and greater influence upon all the institutions of society, as they further infiltrate and subvert those institutions, using them to put forth propaganda and lies to brainwash people. The institutions become so corrupt that they now push forth only lies and propaganda, which were able to brainwash entire generations because of their monopoly of control over all mediums of information sharing. Let's also say, purely hypothetically, that a new medium for information sharing is invented (we could call it "the internet"), which lets average people talk to each other outside the confines, control, and censorship of the mainstream media. This new medium allows people to discuss the truth, to spread the truth, person to person. Over time, this discussion of truth wakes more and more people up, not just to the overt lies, but to the small ones, and to the big ones that have been fully ingrained into all of society by this point.

In this purely hypothetical scenario, the brainwashed masses, merely by discussing and spreading the truth, will ipso facto participate in a purity spiral towards truth, because they only things they're getting rid of are lies and propaganda, as they move toward truth, the truths which were abandoned and censored as the evil people in power began to exert control over information sharing.

This doesn't necessarily mean that all the posited alternatives are true, but it does mean that the outright lies are being rejected, which necessarily will mean that, purely from a numbers game, more truth will be embraced than not, if the people had remained in their previous position of being entirely brainwashed by lies.