Does the blame for Zeke's Attack on Titan euthanization plan lay with his father, Grisha Jaeger? When the Beast Titan first reared his furry head in Attack on Titan season 2, viewers assumed he was just another Titan-shifter enemy in league with Reiner, Annie and Bertholdt. Initially, at least, that seemed to be the case, as Zeke loyally served Marley's army as one of their elite "Warrior candidates." Secretly, however, Zeke has been plotting an end to Marley and Eldia's war, wisely keeping the army's superiors in the dark about his royal heritage.
Zeke's goal isn't revenge against Marley or victory for his Eldian people; he simply seeks an end to the violence and bloodshed brought about by Titankind. Recognizing that violent means wouldn't justify those ends, Zeke hit upon a supposedly peaceful solution - using the Founding Titan's godlike power to render all Eldians infertile. Referred to by Attack on Titan as the "euthanization" plan, Zeke's idea would mean Titan DNA dies out gradually across a generation, washing away all the problems those big nude monsters bring. The citizens of Paradis Island are, understandably, less than delighted about having their future stolen away but, fortunately for them, Zeke can't strike straight away. He has the royal bloodline, but Eren Jaeger holds the Founding Titan proper.
Zeke may be the mastermind behind Attack on Titan's euthanasia plan, but should the finger of blame be pointing toward his father, Grisha? Attack on Titan season 4's flashbacks revealed that Zeke's childhood - as the son of a royal mother and a Restorationist leader father - was not a happy one. Grisha is especially guilty of abusing Zeke on an emotional level - only ever interested in how his son could help the Eldian cause. Grisha neglected his fatherly duties harder than the fandom neglected Gabi after she shot Sasha. He brutally pushed Zeke toward becoming a Warrior candidate and infiltrating the Marleyan military. Grisha exclusively treated Zeke with this political aim in mind, never once concerning himself with the boy's well-being or whether he actually wanted a Titan stuffed inside him.
Zeke's unloving childhood explains why he's pursuing the "euthanization" plan so feverishly in Attack on Titan season 4. Grisha never showed his son the love of a parent, valuing Zeke exclusively as a tool of war, rather than a young boy with a bright future. As a consequence, adult Zeke in Attack on Titan's present day doesn't understand what it means to have and raise children. He doesn't grasp the bond most parents possess with their offspring, and perceives children simply as the continuation of a bloodline. Zeke believes his plot to sterilize Eldians through the Founding Titan is a perfect, peaceful solution to Attack on Titan's endless war, because he's psychologically incapable of seeing how barbaric and cruel the euthanization truly is. And that's all down to Grisha Jaeger, whose colder-than-iceburst parenting style left Zeke no chance of comprehending the true gravity of his Founding Titan proposal.
Grisha Jaeger sure has plenty to answer for in Attack on Titan season 4. Not only did he traumatize Zeke so badly the Beast now thinks sterilization is the "humane" solution, Grisha also forced the Founding and Attack Titans upon his second son, Eren - the one he raised properly. Dying way back in Attack on Titan season 1, Grisha won't be able to face his sins before the anime series comes to an end. But because Grisha once held the Attack Titan, he's connected to the same Path realm as Eren and Zeke. Grisha Jaeger could yet face a reckoning before Attack on Titan wraps up.