system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why were there so many recorded serial killers in the 60s, 70s and 80s as opposed to the present day?
gpt
There's a lot of theories I've heard. 

First violent crime rates in general were much higher back then. 

There's a theory that lead based gas in the 40's-50's lead to more cases where children would get lead poisoning and be more violent in the 60's, 70's, and 80's. 

Gay sex was much more of a taboo and lead to some violent gay serial killers who didn't have an outlet. John Wayne Gacy and Jeffry Dahmer may have managed a normal life if being gay was more accepted, probably not, but it may have contributed to them becoming killers.

In general it was easier to get away with several murders before you got caught. A lot of serial killer stories you can read about how much the police botch their investigation into these guys. Also it was hard for different law enforcement agencies to communicate, so traveling from state to state killing people made it easy to get away with it. 

People were more trusting, hitch hiking was considered a normal form of travel for many years, and often a way serial killers got their victims. Other times serial killers would ask for help moving furniture or something and trap people. Ted Bundy would pretend to have a broken arm and ask women for help moving things. Ed Kemper practiced picking up hitch hikers for months before he actually killed anyone. 

There's probably even more factors than that.