What's new is the ability to quickly spread information. In pre-social-media age, we had "fake news", but outside of newspapers and TV, any rumor would have to spread by word of mouth - and even with phones, it places a significant upper limit on the number of people one person can spread it to.

But with modern social networks, a single mouse click can send it into dozens of feeds; hundreds, for some people. And then you get this effect magnified manyfold:

https://www.youtube.com/watch?v=rE3j_RHkqJc