Attack on Titan has been a rollercoaster, and not just because of its shock value. The drama is quite character driven with betrayals, broken families, and no shortage of manipulation. The main cast has developed from children to adults, and there is no doubt that the trauma of their youth has affected their minds. Some appear more affected than others, with Eren being the most changed.
Eren has now become the main villain of Attack on Titan's story, deeming all societies outside of Paradis Island to be enemies that should be put to death. This conclusion brings up a lot of questions as to Eren's character, such as when was the turning point that put him on this deadly path and whether he could have turned out differently. What happened is the perfect storm, combing both nature and nurture to make Eren this way.
Hints From Childhood
Eren becoming a villain may not have been surprising for fans that paid close attention to his behavior as a child. The most telling scene actually dates back to when he first met Mikasa. He was very young, but still managed to kill the intruders in Mikasa's family home. He did it with ferocity and little fear. When questioned from his father about it, Eren said something very important in understanding him. He told his father he did not kill people, but animals.
This scene is major for what Eren becomes, because it shows a disturbing ability to turn off a switch in his head to dehumanize people. Dehumanization is a big theme in Attack on Titan, as it is what makes Marley attack Paradis. Reiner, Annie, and Bertholdt came to Paradis expecting "island devils" because of Marley's dehumanization. Gabi is the same way. However, they were this way due to propaganda and grooming from a young age. For Eren, this ability to dehumanize others with ease seems to be part of him. It was not taught.
The Perfect Environment
It takes more than what someone is born with to make them become a villain. People are also products of their environment. While someone like Eren could dehumanize people easily, he could have been taught that dehumanization is actually bad and learn how to have more empathy for outsiders. However, in Attack on Titan, the opposite happened. Instead, Eren's ability to dehumanize outsiders was supported and even nurtured by his military training. At the time, the military was not completely aware that Titans were actually people following orders and made by Marley. By the time identities were revealed for the Titans, it was far too late for any empathy.
Eren was not only supported, but elevated due to his Attack Titan power. This means that Eren not was treated like an average scout. He was special and grew up with a lot of pressure on him to be the solution to the Titan problem. While he had friends, none of them were able to really share that burden with him on the same scale. For a long time, his ability to dehumanize was considered a strength and was never questioned. Since he was a protagonist, it was easy to mistake this character trait for just having a big sense of justice. The truth is that dehumanization is dangerous, and can make people into monsters.
A frustrating situation Eren had to deal with was his end goal, as well as the end goal of the military. The more they explored, the further the end goal was. At first, it was just about securing the borders and having the freedom to see the world. Then Marley came into the picture and everything turned on its head. Eren had to take bigger and bigger steps to get the end goal of freedom. All this mixed with his ability to dehumanize others makes it easier to see how Eren developed the sinister idea to just kill everyone outside Paradis.
Could He Have Turned Out Different?
Eren becoming a villain involved a lot that makes Attack on Titan what it is. For him to have not gotten to this point would, a lot of environmental changes would have needed to occur. His ability to dehumanize is a part of him, as shown in his childhood, so that cannot be changed. What could have changed is how he was treated and educated by others. Rather than have his dehumanization be encouraged, he could have been taught differently. However, his ability for dehumanization was integral for winning fights with such ferocity. It is possible that without it, a lot more people would have died.
How Eren turned out is a consequence of war. The best bet for him to have not become a villain was for there to be no titans in the first place. However, without titans, he never would have even been born. He is so wrapped tightly around the titans, it is as close to destiny as one can get. There are even theories that Eren has limited free will because of the Attack Titan's power. It is possible that the Attack Titan itself is a force that is driving him this far. Consuming the other titans has probably only made Eren's mind all the more scrambled.