What types of situations could cause a contemporary American town to become afflicted by a general hysteria besides witchcraft?
In the 1980s, when little was known about AIDS and HIV, a young boy named Ryan White contracted the virus through a blood transfusion. He was a hemophiliac. When people in the community found out about Ryan, they panicked. What if he breathed on their kids at school? What if they drank out of the water fountain after him? Even teachers signed a petition to ban him from attending their school. His family filed lawsuit after lawsuit and finally moved.
Anything that scares us badly enough could make us behave just like the people of Salem.
What created the hysteria at Salem? Historically, many things were going wrong with the Puritan community. This was a culture on the edge, physically as well as politically; besides a few villages up and down the coast there was nothing but wilderness, Indians, and French, who attacked throughout the 1600's; the wilderness became associated with evil. The company that governed the Massachusetts Bay Colony lost its charter; for several years there was no government, creating in many instances conflicting land claims between neighbors, as deeds may or may not have been valid. Good harvests were few, bad harvests disastrous; some historians suggest that the amount of ergot, a form of mold that grows on rye, became concentrated due to a particularly wet climate in the early 1690's. Ergot is a hallucinogen. Almost all the girls who started screaming were from the northern part of the colony (now Maine) where the Indians obliterated all English and English settlements; some claim these girls suffered from a delayed stress after witnessing massacres at a young age. These factors would not be currently applicable to contemporary America, but if simultaneously food became scarce, aliens attacked and murdered people in their homes, the government collapsed, avarice among neighbors increased, children witnessed atrocities, or in other words, if a culture is stressed enough, something like hysteria exists. People are people, no matter from what era.
A very real situation that causes the same kind of hysteria as the witchcraft trials did in Salem would be an incident of school violence. I've never witnessed one personally (thankfully), but from the research I've done, when something like this happens, people want answers. They're quick to point fingers and want someone to blame. When they have someone or something (parents, friends, bullies, drugs, administration, video games, whatever), society can jump on that things or person and persecute it/him/her to no end, even if there's little to no evidence to justify the claim.
People want answers for things they can't explain. Why a 14 year old would bring a gun to school and shoot other kids or teachers is unexplainable, especially if the fourteen-year-old isn't available to give answers. So when people can find an answer that makes them feel better and can "punish" that answer (firing principals, denouncing video games, hanging witches...), the response becomes hysterical.
The Dixie Chicks Backlash.
After 9/11, America, feeling shocked and scared, had a bout of intense patriotism. Everybody tried to show how 'American' they were by putting up even more flags and supporting the 'American' way of life. Unquestioning support for the president went to unprecedented levels. Just after the invasion of Iraq, Natalie Maines of the Dixie Chicks criticised George Bush in public at a concert in London, she said, "we're ashamed the president of the United States is from Texas." and unleashed a storm of mindless public anger and panic. People organised public burnings of Dixie Chicks CD (Medieval or what?) Thousands publicly ranted about the 'deeply unAmerican comments' and boycotted any radio or TV that played them. Scared of being considered UnAmerican, most people toed-the-line and loudly damned The Dixie Chicks. All radio-stations and TV music stations, instead of showing moral character, bowed to mob pressure and took The Dixie Chicks off their playlists (which is a very scary fact). There is footage of parents encouraging small children to angrily throw CDs on burning piles of D.C. albums. It went so far that Natalie Maines received death threats.
Of course, the irony is that Maines was excercising her right to free speech (a very American thing). The Mob behaved in a deeply UnAmerican way while claiming to represent America values.
4 years later, everyone was publicly criticising George Bush.