"You knew exactly what to do, you always did. When Joker blew up the chemical plant, you knew certain compounds in the blast could react with the chemical materials, creating an unrivaled chemical concoction. You knew he was here for that, and took delight in it, yet you ignored him..."
"You knew Mr. Freeze's ice could even freeze the sun. You knew he so desperately wanted you to throw yourself into the sun, to reveal a super nova, a falling star."
"You knew Scarecrow could change Earth's atmosphere, evolving the human race into more powerful beings, giving them bodies better equipped for oxygen absorption, smarter minds, and turning everyone into unequalled geniuses. You knew, he was expecting you to make it happen."
"You knew Gotham was not your obstacle, but your treasure, just as the Earth is mine. Yet, you cruelly and cowardly disregarded their potential, treating them merely as criminals."
"No, it's not because you hate them, and it certainly isn't because you are good or moral. It's simply because you lack ambition—you aren't greedy enough."
"Arrogance is the only reason you're here." Greed took a deep breath and said with a sobbing tone, "You should be greedier than greed itself, but you act like a coward, a disappointment to all the greed."
"Please don't do this, Batman. Don't destroy the me inside of you; don't leave me sobbing helplessly, despairingly in the small corner of your Thought Palace."
"Now, go open those cell doors, embrace him, embrace what you could accomplish under his guidance, love him, become one with him, just as you did with arrogance."
"Don't cast me aside so superficially. Don't condemn me as the original sin as everyone does—If you can accept arrogance, you can surely accept me..."
"...you will accept me!"
As Greed's voice echoed through the theater, Batman realized that Shiller was not Joker, but a different entity—something more reasonable and insane.
If Batman had to provide an exact answer now, it would be like countless games he has played with the Joker, and countless times Joker has questioned him. Shiller isn't the Joker himself, he is the very essence of humanity.
Shiller represents the unrestrained side of one's humanity that can sprout from deep within at any time.
As much as Batman loves the sun, as many times as he has dreamt about the intoxicating warmth of sunlight on his skin, he despises it for being a star that was born simply out of luck, never shinning over him.
But greed told him, not Shiller's greed,but his own, that he has the wisdom and the power to bend the sun to his will and have it under his control.
If he wishes for the sun to shine on Gotham, it must. If it isn't bright enough, then Batman would replace it with a different star.
It's not difficult. Because, he is Batman.
The principles he adhered to and was ridiculed for – revolving around a single city, not killing, not being cold hearted - all boils down to one light phrase, he is not greedy enough.
It all comes down to his lack of ambition, wanting too little, not being able to release his inner greed, which the world considers a sin, like Shiller.
Inside the theater, as Batman turns his head, he doesn't see Shiller's greed, but another version of himself.
A representation of his horrible greed, which he never lost or indulged.