This is a case of bad defaults - why should a developer be required to write code, even if it is a one liner, to _disable_ debug? It should be the other way around - you write a single liner to enable debug.
When it was released and we tried to use it, it broke our site entirely due to third-party libraries we were using.
> Note: by default, React will be in development mode. The development version includes extra warnings about common mistakes, whereas the production version includes extra performance optimizations and strips all error messages.
> To use React in production mode, set the environment variable NODE_ENV to production. A minifier that performs dead-code elimination such as UglifyJS is recommended to completely remove the extra code present in development mode.