It's not. Everytime there's a new form of media or communication there's an uptick in "bad actors". Think yellow journalism or any of the moral panics around TV programming. Even back when the printing press was invented there was an uptick in troll behavior. One of the Green brothers posited that martin Luther was really just a pamphlet troll.
With social media and the Internet, stupid just got louder. I don't think people got stupid.
IQ tests are administration-sensitive and have changed dramatically since the beginning of such a Flynn effect study. The population makeup of many countries has changed in recent years to include many immigrants for whom the study would make exceedingly little sense to include. IQ tests do not cover and do not claim to cover a comprehensive view of human intelligence, famously lacking verbal and social components entirely. It is possible past IQ tests were simply overtuned and we’re now seeing the natural correction.
Amplifying stupid can be very deadly, though. In some sense, the printing press caused the 30-year war, and radio brought us World War II. Eventually, society will adapt. I just wish we could find a way to adapt faster than the bad actors do.
Just to be clear, that "speed-up" is not a good thing: Those 100 years were a lot less deadly in total. The World Wars were even shorter and much deadlier still. A possible next full-blown conflict between major powers will only last hours -- and end civilization.
With social media and the Internet, stupid just got louder. I don't think people got stupid.