Yeah, 25% is way too low a threshold for brainwashed to be useful to those at the top. They need at least 50%, 70% would be good but 90% is ideal. Society being defined as in peril is basically a rhetorical constant however.
On a more serious note haven't societies long been based upon common brainwashing? The Bronze Age and before are fuzzier on the details but propaganda certainly existed then as well at a smaller scale.