Other coastal cities such as London, St. Petersburg, and in the Netherlands already have coastal flood defenses just as elaborate and just as expensive.
There's nothing stupid about building flood barriers for NYC - they will end up being less expensive than the damage from future storms.
The STUPID thing is saying they're needed because of global warming. They're actually needed because NYC is a coastal city in an area that's been exposed to powerful storms for 10,000 years.
I have no problem with sea walls, just the global warming excuse.
However you can rest assured they will be incredibly expensive and built by companies with political connections, and not like in South America where they are built and maintained with convict labor.