Kingdom Hearts isn't about light or darkness, it's about love

Other than the series always thematically showing that love is the ultimate answer and power, even more so than the power of light or darkness, here are some quotes:

From Kingdom Hearts Birth by Sleep:

Aqua: "A pure heart filled with light... It's strange, the Master taught me darkness needs to be destroyed. But how, if not with light?"

Fairy Godmother: "Oh, my dear, you're too young to know. Experience more things, and you'll find the answer. Just trust in your dreams."

(Fairy Godmother implying the only way to defeat darkness other than with light is with love.)

From Kingdom Hearts Birth by Sleep:

Yen Sid: "I will tell you what your friend needs right now. It is not your protection. He needs you to believe. You see, Ventus's heart hangs in the balance. It sleeps in the place between light and darkness. From all I can perceive, that means he will be looking for a friend--one who believes in him, to show him the way home. Just as long as you love him...then Ventus will be able to find you when he wakes. He can follow that love back to where he belongs--the realm of light.”

(Yen Sid implying the balance between light and darkness is love and that love is the only thing that can lead Ventus' heart home.)

From Kingdom Hearts Chain of Memories:

Riku: "What are you making me choose now?"

DiZ: "Between the road to light and the road to darkness."

Riku: "Neither suits me. I'm taking the middle road."

DiZ: "Do you mean the twilight road to nightfall?"

Riku: "No. It's the road to dawn."

(Riku not choosing light or darkness, but choosing what he calls "dawn.")

From Kingdom Hearts 3D: Dream Drop Distance:

Riku (to Ansem, Seeker of Darkness and Young Xehanort): "I walk the road to dawn!"

Riku (to Ansem, Seeker of Darkness): "Consume the darkness, return it to light.”

Young Xehanort (to Riku): "I don't know how you did it, but you really have found a way to trap darkness inside your heart. And a boy who's immune to darkness is of no use to us."

(Riku reaffirming that he wields both light and darkness, and that he turns the darkness into light. That is the state he calls "dawn." And Young Xehanort confirming that by walking the road to dawn, Riku has somehow become immune to darkness.)

From Kingdom Hearts 3D: Dream Drop Distance:

Data-Ansem the Wise: "The heart has always been quick to grow. Each exposure to light, to the natural world, to other people, shapes this most malleable part inside of us. Nobodies are not different from us in that manner. Sora was the only one able to return to his human form without destroying his Nobody. That is a statement to the love in his heart for other people, and the bonds that tie them together. Perhaps...he has the power to bring back the hearts and existences of those connected to him—to recreate people we thought were lost to us forever. Our most precious treasures—even an empty puppet—the trees of the forest, and the petals on the wind—there are hearts around us everywhere we look. And it does not take superhuman powers to see them. Surely we remember as children the way our hearts made everything seem so shiny, and perfect. Sora has a heart like that—uncorrupted, willing to see the good before the bad. When he sees the heart in something, it then becomes real. When a connection seems broken, he may have the power to mend it. He has touched countless hearts, he has accepted them, and he has saved them. And some of those hearts have never left him—whether they fell into darkness or were trapped there—whether they sleep in the darkness of Sora's heart, or were welcomed into its warmth—they can be saved. All Sora needs to do is be himself and follow wherever it is that his heart takes him. It is the best and the only way."

(Data-Ansem the Wise saying that Sora's uninhibited undying love for people and his willingness to always see the good before the bad in anyone or anything is the ultimate answer that could solve everything and save everyone.)

From Kingdom Hearts III:

Ventus: "I didn't ask for this. To be sifted apart nice and neat. We should be free to choose. Not just light, not just darkness. We decide what we are."

(Ventus implying light and darkness are choices and you can choose to be both or neither.)