Since I've been thinking a bit about propaganda, let me share a thought. For some time now I've been bothered by public health campaigns (or other education campaigns) that don't tell the truth. One example (suggested by my sister-in-law) is the much-mocked "This is your brain on drugs" tv ad. It's a striking visual metaphor: cracking an egg onto a hot frying pan. But is it truthful? It refers to "drugs" (presumably illicit), but which ones? What's the evidence that they "fry" your brain? Perhaps your brain has to already be fried before you'd consider using them. Or perhaps some of the drugs actually enhance your brain. But I don't think that truthfulness was the point of the ad. It was meant to convince, not to genuinely inform. And how do you convince people? By using the techniques perfected by Joseph Goebbels, the Nazi Minister of Propaganda. Ok, maybe that's a cheap shot, but I think propaganda is a dirty business.
As a matter of principle, I think that public health campaigns should tell people the truth. I remember with HIV/AIDS the "safe sex" slogans that eventually gave way to the more honest term "safer sex". From a pragmatic standpoint, if you tell people something, and then a little later admit that "maybe that wasn't quite true", you risk losing credibility. Sometimes you'll hear someone say something condescending like "people can't handle the truth." What's that supposed to mean?
One objection that may be raised is that you have to simplify things to communicate with the public. I don't dispute that, but you can still tell the truth. If you need to simplify something you can provide an indication that that's what you've done (and perhaps suggest where to get more details).
Another objection might center on the word "truth", which of course opens up a whole philosophical can of worms. When Jesus used the word, Pontius Pilate replied "What is truth?" But it wasn't an honest question, it was jaded cynicism. Without denying the complexity of the question (when asked honestly), I think it can be provisionally set aside by saying that "the truth" means what one honestly believes to be true. I don't deny that that sounds circular.
Advertising is an inevitable aspect of the marketplace. But the marketplace shouldn't rule supreme. I can accept that marketers will influence my choice of shampoo, but I don't think they should be involved in the content of public health campaigns!