To understand why a helmet should not be removed from an injured motorcyclist, it is important to consider the following reasons:

- **Spinal protection**: In the event of an accident, it is crucial to keep the injured person's neck and spine aligned and protected. Moving the neck abruptly or incorrectly can cause serious spinal injuries. The helmet helps maintain the stability of the head and neck, preventing movements that could worsen the injuries.

- **Rescue rules**: When assisting an injured person, one of the general rules is not to remove the helmet. This is because the helmet provides support and protection, and removing it without proper knowledge can result in involuntary neck movement, increasing the risk of spinal damage.

- **Act with caution**: If it is necessary to move an injured person, it should be done very carefully, ensuring that the head, neck, and body remain aligned as a block. This minimizes the risk of additional spinal injuries.

In summary, the helmet not only protects the head from impacts but also plays a crucial role in protecting the spine by preventing abrupt neck movements. Therefore, it is essential not to remove it from an injured motorcyclist.