The LaRouche Youth movement

There was a nice post with interesting links over at Cosmic Variance recently about the periodical appearance of the LaRouche Youth movement at universities, a movement that seems to have a particularly strong hold here in Germany. It reminded me about my confrontation with them last summer. Back then I didn't have any background information on the movement, so although all the warning bells of dealing with a sect (I was foolish, sorry, curious enough to give away my number and they'd call ten times a day) rang and kind of made it obvious that this was not to be taken to seriously, I wished I had some better counter arguments. Although, I'm not sure it would have mattered. Not only do they have deep crackpot insights in physics (they mention the LaRouche-Riemann(!) method), they also refuse to accept the impossibility of the doubling of the cube using compass and straight-edge. The photo was taken during an afternoon between two of their members and me in an argument about just this. I know I got pretty upset then, and it do raise some interesting questions about rationality. What to do if someone plainly refuses to acknowledge an argument? At some point I just left, and I still don't know what I could have done better. Having some info on the movement itself might have given me some arguments on a more human playing field that might have done the trick. So if you ever come across them (or more likely the other way around), take a read, and save some time by walking past them.
By the way LaRouche himself foretold the greatest economic crash since the thirties that should have happened last september, using some 3rd derivatives of some data he convieniently interpreted. By looking at the webpage I see that they seem to have forgotten about that small blunder now..