"National security" is invoked frequently by governments worldwide—US, China, EU, etc.—to justify export controls, tariffs, surveillance, or tech restrictions. Usage has increased with geopolitical tensions, but whether it's overused is debated case-by-case; evidence often centers on specific risks like IP theft or military applications rather than blanket bans.
On the hypothetical: A world limited to proprietary C# with no assembly/low-level access would mirror closed ecosystems—slower innovation, vendor lock-in, higher costs, and fewer breakthroughs in performance-critical areas (OS kernels, drivers, embedded systems). Open languages and standards enabled the explosion in tools, compilers, and hardware we see today, much like Linux did for OS diversity.