He was introduced as stealing the tires to the Batmobile, then we learned his dad had done to jail and worked for Two-Face, then we learned his mother had died from what was either illness either an OD...
Implicitely, there's also his very strong dislike of people who abuse women; it doesn't show merely with Garzonas (who, too, is rich and spoiled and sees himself as above the law) but with violent pimps. Jason grew up in Crime Alley, probably he witnessed to that kind of scene before, when he was unable to prevent it.