The 1,050-foot-tall MoMA Expansion Tower will start rising on West 53rd Street in 2014—holding 145 luxury condos and 36,000 square feet of museum space. Maybe it's mistake, but not for the reasons you imagine.
You can't stop building the future...
This city was built on the desire to create a new world. It respected nothing. It happened for no other reason than the fact that some people imagined it had to exist—like the Big Bang creating the Universe. Forces collided, creativity exploded and change was never-ending, a permanent metamorphosis from worm to butterfly to seven-head hydra, a cycle of creation and destruction that never stops. Etc etc.
It was great while it lasted. That's what gave us this incredible place, despite the original naysayers. You know, some people once hated and mocked the Empire State Building when it was built. Now everyone on the planet wants to go to the top to take a photo, because the Empire State Building is fucking amazing. It's the symbol of all that was modern about this city. No fear of change, of growth and chaos.
New York will keep expanding upwards and around. It can't happen in any other way. New York should be like Shanghai and keep destroying old buildings to build newer and higher and cooler ones. It seems like the only logical path—change is has been NYC's DNA since the 17th century.
...but we are doing it wrong
Perhaps you can argue that these mega-buildings will reduce the quality of life of New Yorkers by blocking the sun in Central Park, like Jacqueline Kennedy Onassis said in the 70s, stopping a building from happening in the process, but the problem is more tangible than that.
The real trouble is that New York can't keep growing at this pace with infrastructure built at the beginning of the 20th century—now nearly on the verge of collapsing. Think about this staggering factoid: the city just opened the first new water tunnel in a century, allowing it to close the ones that were almost in ruins for repairs. Or just remember what happened with Sandy. The Metropolitan Transport Authority's tunnels are still using water pumps used in the construction of the Panama Canal in 1914. If they fail, the entire subway network would get flooded.