Because harassing passengers with fake bags of cocaine really keeps everything "safe" : Story
This is a great piece about the TSA, written by Geoffrey Goldberg. He echoes the general sentiment that the new pat-down checks are designed more to embarrass you into stepping into the back-scatter machine than to provide any form of security. If enough people actually opt out, the TSA won't have the balls or the staff to feel up everybody because there will inevitably be lawsuits.
So make them feel you up - the more people who do it, the worse it will get for the TSA. Make them uncomfortable. Take up their time. Be an inconvenience to them. Treat them like they treat us.