A great point even if its clumsily stated. I think here's perhaps a little bit better way to say it:
Never fully believe your own propaganda, even when it's true. Always reserve some emotional detatchment apart from that truth just in case, as often happens, its meaning shifts.
"It is impossible to overstate how wrong BLM and reform activists were on this count."
I have been a successful propagandist, and I have thoughts about this. Believing your own propaganda too much is risky even when it's true, and extremely dangerous when it's false.
This is a chronic problem with left-wing propaganda. In an ideal world, or at least an ideal world from the point of view of a left-wing organizer, propaganda would usefully deceive and demoralize everyone outside the movement while the movement itself remains in contact with reality.
But it doesn't work that way. Really skillful propaganda has the emotional hooks to deceive everybody, including your own people. This divorces them from reality and sets them up for rude shocks when the divorce is no longer deniable.
I never had this problem, because all of my propaganda was written to make the truth attractive to people who had previous incentives to reject it, rather than peddling a lie. Even so, I knew I had to remain skeptical of my own assertions in order to avoid veering off into cloud-cuckoo-land.
The American left doesn't have this luxury. It desperately needs people to believe that the US is a profoundly racist and unjust society in which cops regularly brutalize Black people for no reason. Which...isn't true. Cheap ubiquitous video has demonstrated this.
If propaganda worked out in the ideal way, leftists would successfully demoralize others by making them believe this, but retain the ability themselves to deal with the actual fact that Blacks stopped by cops become semi-psychotically violent with enough frequency to justify much more violence than the cops routinely exert.
It hasn't worked this way. Because "reform activists" get caught up in their own propaganda, many of them are now reduced to crying that police interactions should *not*? be recorded. Which is absolutely not a position that's going to convince anybody outside their own movement. That position looks like it's designed to give activists room to lie about the problem, and it looks that way because it is that way.
I repeat: never fully believe your own propaganda, even if it's nothing but an emotionally compelling presentation of the truth. For that way can lie madness.