If I may interject here -
Pissing them off may not be the best way to approach this. I would suggest educating is a better option.
If you want these parents to understand what they are involved with, and what is happening to their kids - you need them to listen to you - and people tend to tune out those they are pissed off at.
Of corse, as Karen Lile experienced, attempting to educate them will piss most of them off - but there will always be those few who will listen and they may get the ear of a few more.
No one will listen if you come across as exactly what they are afraid their kids will become with out the program.
But protesting a seminar site is a pretty good idea.