PANAMA CITY, Panama—One of the things that shocked me the first time I talked with an active cartel member in Mexico was hearing how much he loved his work. But as time went on, and I interviewed others like him, I came to see that my initial surprise derived from my own naiveté.

In fact, almost every time I’ve spoken to a sicario, as the cartel assassins are called, or a comandante from a paramilitary crime group I’ve gotten the same message: they truly enjoy what they do.

The homicide rate in Mexico has risen by almost 30 percent over the last five years, a national epidemic. There were at least 25,316 murders in 2017, making it the most violent period since the Drug War began. So far 2018 is on pace to eclipse those numbers.