Of what value is it take on the archetypal role of witness to large scale atrocities (such as war or genocide)?

I just finished watching this documentary about UN General Romeo Dallaire who was basically hung out to dry by the western world (as was Rwanda) during the genocide of 1994. While he was not physically threatened, he suffered personally and greatly due to his being set up to fail but did his best to save who he could and serve as a witness to the rest. (While we’re on the subject of Africa, Darfur also has many witnesses.)

Similarly, this documentary trailer about a famous war photographer makes a sincere attempt to answer the question.

Lastly, this book attempts to turn over the stone of the Russian gulags, which systematically killed millions, during the time of Stalin.

It is obvious that these witness accounts do little to stop atrocities in their progress, and they do not prevent future atrocities from happening. The best they seem to do is to provide some assurance of the truth of the event for anyone who happens to care or was involved, but seem to be of little utility for anyone who is not directly affected. Most consistently, it seems, these witnesses do it to give themselves solace or for idealistic notions of change, which often do not pan out.

Personally, I believe all these events are wrong and evil and would prefer they not happen. Still, I get entranced by their mind-boggling scale (for example, pondering how an entire nation could perpetuate the imprisonment and forced labor of 20% or more of its citizens for multiple decades and how it was so pervasive that citizens kept a backpack at their front door in preparation for their inevitable arrest), and I also find myself somewhat enamored with storytellers such as Dallaire, Nachtwey, and Solzhenitzen.

Is witnessing a fool’s errand? Is its value limited to those who experienced the event more or less directly? Is it a better use of one’s time and energy to focus on something other than the episodic steamrolling of humanity?