Fandom: DCU (ish)
Summary: Juggling identities doesn't come without a cost.
In many ways, his favorite identity is Clark Kent. He has no powers, but he has friends and loved ones, and is as nobly dedicated to his work as any superhero could be. It's a life he wouldn't mind living for real.
But he can't. There is too much he can do to help, and if the price of having that help accepted is dressing in primary colors and acting condescendingly aloof, so be it. It'd be selfish of him to put his emotional needs above those of his adoptive planet.
And Superman at least is a symbol of hope for Metropolis and most of the world. There are places like Gotham City, too cynical to see Superman as anything but a fool or a flying target. Places that answer not to truth and hope, but to greed and fear. Places that need a Bruce Wayne and a Batman.
J'onn doesn't enjoy playing those parts, but he understands their value.