You're right, it doesn't seem right. On the other hand, many injustices exist because one injustice cannot be eliminated without creating another. I selected the words of Darwin and M.L. King Jr. because those words are of tremendous value to society. Note that I say the words, because those words are as important as the ideas. The reality is that you can rewrite Darwin's ideas and King's ideas and still get the point across. The reality is that you can improve upon those ideas in the process of rewriting them, because we know more about biology and social equity today than we did in the past. Yet those original words carried a lot of power. They carried so much power that we still talk about Darwin and King today. We use those words to ensure that their legacy continues to live.

In my mind, it would be a grave injustice to society if those words were in private hands rather than being treated as a public asset. Just as we have roads, and libraries, and hospitals, and parks as a public trust we should have particular words from particular people being held in a public trust. While many people profit from the availability of roads, libraries, and hospitals we do not let one entity do so. (By that I mean businesses use roads and libraries, healthcare exists as much to ensure a healthy workforce as it does for compassionate reasons.) Why does the same have to be true for every word written over the past 100 years?

Now I'm not saying that every author, or orator, is as valuable as the examples that I brought up. Yet there are certainly many authors who have made valuable contributions, even "best sellers" of times gone by. It is probably easiest to let every authors words slide into the public domain and let society choose, rather than fighting to appropriate those words in specific cases.