No, it isn't. It is harmful for free software projects to blindly incorporate software with incompatible licenses. It is not harmful to write software with incompatible licenses. Most software written is incompatible with Debian. With very few exceptions (for instance, the sole-sourced drivers to popular peripherals), none of it actively harms the project.
Debian is not entitled to Douglas Crockford's work and therefore Crockford cannot harm Debian through incompatibility. Someone else can write a replacement JSON library; it's an intern-level project.