Bad Science comes in many forms, from Moon landing deniers to creationists. It's not my field, but I would guess that the biggest impact is on the health science. There, bad thinking literally kills, and it kills thousands every year. Millions? Maybe. The flavors of health folly are as varied as the fields of health science itself: HIV-deniers, anti-vaccine promulgators, homeopathists, diet fads, and on and on.
There are the Good Guys too, out there to strike down what they know to be off ill health. But you will rarely find one of the caliber of Ben Goldacre (of BadScience.net), who takes down the huge corporation of one Gillian McKeith in an article in the Guardian. McKeith is a person of Sylvia-Browne-sized capacity for misdirection and misinformation, and has the potential to do a lot of harm. Good thing people like Goldacre are around.
Read that whole article to see how it's done, folks. But here's a great money quote:
"Ignorance is like cholera," [Sir Muir Gray] says. "It cannot be controlled by the individual alone: it requires the organised efforts of society."