Fear

It's one of the key ingredients of woo. Health scares try to convince people that trace amounts of everyday chemicals or life-saving medical practices will irrevocably corrupt your pure body (unless you buy their product). Conspiracy theorists try to convince you that the omnipotent, omniscient government is planning to get you sometime next Tuesday. Religious fanatics invent invisible, allegedly inevitable horrors for your soul if you don't bow down to their arbitrary rules.

Fear and panic fuel poor decision making. Dramatic but improbable threats naturally seize our attention more than simple, everyday risks. The former also tend to have an urgency created about them to discourage a potential victim from thinking things through or performing genuine research. This quite often leads to sloganizing statements to spread the word: Don't think about the topic, just spread the word as fast as you can.

For those who dare question the supposed hazard, sowing distrust is the preferred method: Don't waste time debating the actual details, go straight for the ad hominem, make up connections between them and the eeeee-ville establishment out to get you, and denounce open-mindedness towards evidence as too limited and constrained to handle the issue.

This is what we as skeptics are up against much of the time.