It's from towards the beginning of JLA #84-89, the "Trial by Fire" storyline by Joe Kelly in which J'onn finally cures himself of his fire issues by having a villain repeatedly set him on fire until it doesn't bother him anymore, but it turns out the Guardians gave Martians they're fear of fire to inhibit their inherent Martian evilness, onoz. In the scene you're talking about J'onn is making all of the JLA's villains feel guilt as a last gift to his friends before he destroys them all.