The Flash's motley crew of villains, the Rogues, may be a group of criminals, but even they have standards, and their dismissal of Captain Boomerang sums up why Digger Harkness can only get work with the Suicide Squad.
The Rogues aren't like most villains. Unlike the menaces that plague Gotham and Metropolis, Flash's greatest enemies are a strong, united front. Armed with guns and technology that allows them to take on the Fastest Man Alive, the Rogues live by a few rules to keep themselves an efficient unit. They don't kill superheroes, women or children, they don't use drugs, and most importantly, they watch each others' backs. While these edicts were mostly set by the group's leader, Captain Cold, the other members follow and it's kept them in plenty of cash and beer, while also prompting the Scarlet Speedster to go easier on them than he otherwise might.
Related: Suicide Squad Owns Up to Captain Boomerang's Problematic Roots
But not every member of the Rogues could live up to Leonard Snart's standards, and the villain said as much in The Flash #2 by Geoff Johns and Francis Manapul. Digger Harkness, aka Captain Boomerang, has just returned to life in the wake ofBlackest Night. But as a convicted felon, he's returned back to Iron Heights penitentiary where he awaits his previous death sentence to be reinstated. Before long, Digger is greeted by his old pals and he anxiously asks them to help him escape. However, Cold tells Boomerang they aren't there to help him, but to deliver a message. Snart tells his compatriot that before he died, Boomerang had let himself go and became a joke of a villain and because of that, he's lost his privilege of getting sprung by his former teammates.
Cold does offer Digger one more chance
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