User blog comment:Gifist8/The Flash Season 2 Review/@comment-27700324-20160821004934/@comment-3423279-20160822024629

Because Batman (supposedly) needs the Joker just as much as Joker needs Batman, I think this was brought up in a What the Hell Hero moment by Jason Todd.... the Robin that was killed by Joker and later revived for the people who have lived under a rock for about a century.