"Crowds" are more virtual now. Viral marketing follows the same principles, so the idea of manipulation of the masses by a relatively tiny group of individuals is so commonplace these days, that those individuals who are payed to do this manipulation must think these crowd theory videos are quaint, simplistic and adorably naive. Examples of Facebook using data gathered to manipulate masses for a specific outcome are commonplace. Google makes money of people busy trying to make their videos viral to get ad revenue, effectively killing newspaper revenue around the world.
The danger is big-ticket items that have long-lasting effects such as Hitler's success in getting away with the holocaust for so many years and the masses who apparently abandoned all critical thought and went along with it so as not to appear to be outsiders and risk being ostracized (lest their skin be made into lamps).
There are the current protests and riots that have spread where people are looting and you see individuals smashing windows, then we see the politicians outraged at the protesters trying to get buy-in from the public in order to distract them from the endemic problem of the untouchable group-think that cops have exhibited for decades where the unwashed public is the enemy. So that is an example of clear manipulation by a small number to try to get crowds to switch from anger at police mentality to anger at protestors destroying property. Then you see the odd image of cops wearing masks being the ones wielding the window-smashing hammers.
The critical thought aspect of people figuring out what is really going on comes from relatively tiny numbers of people, so it is usually not until after the damage is done that these observations that "the emperor is in fact not wearing any clothes" becomes known. 9-11 getting people to hate Muslims to garner support for the creation of "homeland security" and distracting the masses from the illogic of a handful of knife-wielding terrorists becomes the focus rather than the financial behind-the-scenes machinations.
If you look at history, something like the now-famous Salem Witch Trials, a prime example of "mass" hysteria (keep in mind the population of Salem in 1878 was around 1,200 people I think), you'll read in Wikipedia about 200 people tried, 30 found guilty. The whole town bought into this idea of witches. This was spawned by very few people that had ulterior motives that didn't involve fear of witch spells, but they knew the simplistic nature of their target audience and thus convinced them that hey, "witches". That is a pretty hefty proportion of the population charged. Nowadays, there are some nazi-like strata councils operate in a similar fashion that demand group compliance and you go with the flow or you are stamped into the ground of compliance like the proverbial protruding nail in a Japanese floorboard.
So, old news.