It's all there in the first sequence. Observe how we are thrown rather bluntly into this bleak, shocking scene which the composition of the frame itself, suggests that something horrendous is about to happen. No need for introduction or easing our way into the subject matter. Some material needs to be handled directly, which is reflected in the director style here. It's also besides the point to know of the reasons that lead those people to be in that situation in the first place. However, I think the main and more appropriate question to be asked is: does it really matter?
What follows shows the Protagonist trying to insert meaning into his life, after what he willingly witnessed, through a series of brilliantly displayed short segments of his monotones, empty existence. He is trying to escape the haunting sounds of suffering and dehumanization echoing in his head. He knows he's being watched, he feels guilty somehow so he attempts to trick the observer (consciousness?) by blabbering on about how sympathetic and caring he is to the people around him. When you can clearly tell that they don't even buy it.
What follows shows the Protagonist trying to insert meaning into his life, after what he willingly witnessed, through a series of brilliantly displayed short segments of his monotones, empty existence. He is trying to escape the haunting sounds of suffering and dehumanization echoing in his head. He knows he's being watched, he feels guilty somehow so he attempts to trick the observer (consciousness?) by blabbering on about how sympathetic and caring he is to the people around him. When you can clearly tell that they don't even buy it.