Hey, MAYBE the reason JJ hates vigilantes is because his wife's death was caused by the recklessness of one!
During his younger years, JJ was in college and working multiple jobs to support his studies and his son, who was born out of wedlock. One day, he and his soon-to-be wife were on their way to a restaurant but wound up in the middle of a gang shoot out when taking what looked like a shortcut! Had it not been for one of the vigilantes recklessly toppling a structure and scaring her off, she wouldn't have ended up with a bullet in her chest!