A "witch-hunt" is making false accusations of someone, or a specific group of people, based on a common fear of the overall community. Check out the following for more information:
Salem Witch Trials
House UnAmerican Activities Committee
Sen. Joe McCarthy
"The Crucible"
McLaren Pre-school
The most recent "witch-hunt" in American history began after 9/11 when Arab Americans began being unjustly targeted as potential terrorists simply because they are Arabs. The community at large allows it to happen based on the common fear generated because of 9/11.