My point...the police (for the most part) know it doesn't work, yet they continue to use it as a 'tool' to trick people....people who think it DOES work....so teaching them that the cops are lying to them (again) about this is 100% appropriate and useful information for them.

I had no idea what you were saying about Africa...let's drop it.
If 1/2 million people (a HUGE number, and yet I think not 1/100 of the likely true number) still believe in them, that's 500000 people out there ready to convict you based on lies...and it's probably 100 times more than that. Americans were told for decades that lie detectors work, and barely told at all that that was all a lie. Many many people believe in them as factual devices, not just boxes to trick people with.
EDIT: The same could be said today for fingerprint evidence...which the public perception is that it's an infallible science (just like we were told about lie detectors), when the truth is it's closer to an interpretive art form than a science.

As to your second post...plenty of people still believe, far more than you give credit for, and these people may sit on a jury. If you have one person who KNOWS that lie detectors work, and 11 who think they don't, but aren't sure, the mere mention of 'the defendant failed a lie detector repeatedly' during closing can put many a defendant in prison....and has.
Again, I think you give the public too much credit, first by saying that only .3% think lie detectors work...I would bet that a survey would show more like 10% still think that, and the idea that the rest of us all KNOW for certain that they don't, and can't be convinced by one of the 10%.
For those, and other reasons, repeating 'lie detectors are liars' over and over is proper and useful to both those who don't know, and those who do.