Why did Eren become the villain?

While Eren has the fates of his comrades and friends in mind, there’s no way he can follow through with such a plan that doesn’t leave him a morally reprehensible character. So, simply put, Eren does become the villain of Attack on Titan. His actions also lead him to a tragic end.

Is Eren turning evil?

While acknowledging Eren’s importance and the nobility of his cause in the beginning, these fans acknowledge that Eren had a complete breakdown, which ultimately led him to become a tyrant and the show’s most dangerous villain.