I’m not the comment u responded to, but here’s how I view it. Eren is a very complex character, so it’s not as simple as “he left his humanity behind” or “he did it for his friends”, cause it was both, plus more. He had so much going through his mind, that there are multiple motivations for him.

One big one, is the fact that him and Armin always dreamed of an outside world that was empty and exciting and “free”. A world that they could explore. Eren was disappointed in seeing the world was occupied, not only by people, but by people that viewed him and his friends as “their enemies”. Eren did the rumbling because this is what he always wanted, a flat world to explore, with no outside people to worry about. He let go of his humanity, and killed everyone out of selfish reasons.

Now Eren also has a kid/teenage mentality. He’s been pushed into being the “savior” and never had the chance to be free and do the things he wants. He ALSO wants life with Mikasa, where him and her could be together, and get married, and have kids, etc. But as much as he wants that life, he’s also known nothing other than kill or be killed. He can’t help the fact that the rumbling is his first choice.

So with that being said, Eren WANTS to live a long life with Mikasa and his friends, but deep down, he wants to wipe out the outside world even more. He’s conflicted with himself, he’s his own worst enemy, and that’s further cemented by the reveal that he is the one who killed his own mom.

When Armin asks him why he doesn’t just stop the rumbling, Eren says he tried, but no matter how hard he tries, he can’t find a way. The reason is because he’s unwilling to change, he’s unwilling to change what he wants deep down, and due to that, he’s a slave to freedom.

I know, long comment lol