“Because he's the hero Gotham deserves, but not the one it needs right now"

most nolan stuff is

it was a terrible quote, made worse by the sequel

"He's a watchful protector.A silent guardian.The Dark Knight".
Cue dramatic music.End credits.
But he just went home,parked the batpod,and went to bed for 8 years.

I think it does sorta make sense and sorta not.

So, I think what it's going for is that Gotham is such a cesspit (although a lot better since Batman Begins) that the chaos of the city "deserves" a brutal, shadowy vigilante like Batman to whip them into shape. They deserve darkness, but they *need* hope so they can get out of the darkness. That's why they're preserving Dent's heroic image: they need Gotham to aspire to something that doesn't need Batman.

Where it goes wonky is that Gordon also lauds Batman and says he's the silent protector and whatnot, so maybe Gotham needs Batman and a Golden Boy. Maybe duality is part of life and part of Gotham in particular? But the quote isn't really saying that.

I think it's kind like Yoda's "Fear leads to anger, (etc.)" stuff where it sounds profound and wise and then you think about it and it might not be dumb, but it's not really Confucius, either.