The biggest part is "multiculturalism" and the internet. I put muticulturalism in quotemarks because what we experience right now isn't honest multiculturalism, its a shield.

Every spate of mass hysteria in history has had a shield or a scapegoat of sorts.

• The Dancing Plague of 1518 - Eerily describes epilepsy but it was also noted that dancers generally did not reside where they danced and regularly took part in fornication, lewd gesturing and so on. This all sounds suspiciously like a rolling party of the 70's needing an excuse to behave in such a manner. Especially as it was during a period in which puritanism was going strong.

• Salem Witch Trials 1692-93 - Four young girls suffering fits sarked a Witch Hunt - Could have easily been manipulated and abused by a small group of people to rid their town or towns of personal aggrievances.

• Halifax Slasher (1938) - found to be a hoax, people were cutting themselves and injuring themselves while blaming a figure who ran around with knives and hammers. Several were jailed for wasting police time. Clifford Edwards found himself facing the entire mob hunting for the slasher, because someone yelled out his name.

The later ones listed by Wikipedia become gradually harder to discern but you can see a similar pattern where one two or even a large group of people took advantage of situations.

One which threw me off was the Laughing Students in Japan, but this could be attributed to mischeivous rebellion on an organised scale.

Ours is no different, the Social Justice club have set themselves up as the Witch Hunters and they run around screaming names, trying to gain traction using race or sex as their shield. For the most part we can see past the obvious attempts but there have been successful attempts at falsely naming people and ruining their lives, careers or even actually causing suicide or misguided murder. http://bluegape.com/activism/saurabh-jain/innocent-man-killed-by-angry-crowd-for-false-rape-accusation/

Edit; Disclaimer, this isn't to say there are periods of genuine mass hysteria, but these generally have a catalyst, quite often an obvious one which dies down shortly after. These ones also generally become conspiracy theories. There was a period of mass hysteria when Princess Diana died, when the Twin Towers fell and so on.