Collectively these companies have raised over $200 million in funding to power what’s known as the “sharing economy.” But there was time not so long ago when the idea of interacting so freely with complete strangers would have made many Americans much more uncomfortable. “There was a cultural moment during the ’70s and ’80s where the dominant boogieman was the serial killer. This figure crystallized our worst fears, and walked among us,” says Harold Schecter, a professor at Queens College and a true-crime writer.

A 2011 study, “Extreme Killing: Understanding Serial and Mass Murder,” found that the number of serial killers in the United States began rising in the 1960s, peaked in the 1980s, and has been falling ever since. “There is definitely an intriguing connection between the decline of serial killers and the rise of this sharing culture,” says Schecter, “These startups reflect how much our anxieties have eased.”