By the 23rd century, his speeches advocating personal freedom were banned by the Terran Empire, as were those of numerous other Terrans who had expressed similar views throughout Earth's history. In 2274, the 13-year-old David Marcus, who was then living on Imperial Starbase 47, was able to procure transcripts of suppressed speeches made by King and others.
When his mother Doctor Carol Marcus discovered these texts, she feared for her son's life as she was aware that the mere possession of such materials might be grounds for David to be tortured to death or publicly executed. Although she considered deleting the texts, she ultimately decided against it when she considered the sheer number of people who had risked injury, incarceration or death to preserve them over the centuries. Instead, she told David that she would allow him to study the texts on the condition that he not reveal their existence to anyone else. (TOS - Mirror Universe novel: The Sorrows of Empire)