The entire point of the Joker's massively tormented (and, may I add, drawn out) return is to destroy the family that has made Batman weak because they humanized him. The Joker strongly believes that such relationships had reduced Batman into an ordinary and fallible man, and since the Joker's vanity is centered around the fact that he is unique and his nemesis is exactly as that too; and they are locked into an eternal battle of will and wits forever and ever (it's worth noting that there are lots of accidental homoerotic layers to the way the Joker pines over the Batman in Snyder's narrative framework), he thinks he's actually doing Batman a favor by eliminating his surrogate children and own son and heir. It makes perfect sense for the Joker to be this possessive and entitled to Batman. There's something vaguely pitiful about it too.
The seventeenth issue, Death of the Family was personally satisfying if you focus on the echoing thematic dissonance between the Batman and the Joker as the dichotomy that they've always been: order and chaos; and placing that in a more humanistic context where they are more than just mere concepts but also people who are afraid to own up and face the flaws of their humanity and how much they have alienated and often damaged the few people who are important to them.
There is that poignant scene where Batman threatens to reveal to the Joker his real identity and the Joker actually flats-out refuses. That for me was a significant look at how the Joker wants to operate; he desperately wants to cut himself off from any kind of humanity including his own, but there is loneliness to that so it would be comforting for him to know that Batman will do the same as well, considering the only lasting and meaningful connection he ever had was with the Dark Knight.
During the run and the conclusion of this storyline, I believe Snyder wanted to reveal just how much Batman and the Joker are intrinsically tied to one another. This for me is also a major milestone among Batman and his children and I'm interested to see how it plays out for everyone concerned since they basically just endured another traumatic event that should re-define their relationships.
* The focal point of this saga is to establish the begrudgingly co-dependent relationship between Batman and the Joker, and how it ultimately affects everyone in Batman's inner circle.