In the manga, for YEARS, it was acting like he had some big plan in the bag.
For the life of me, I cannot sympathize. Very early on, I thought that the story would end like that one Dr. Seuss book about the Sneetches, and then I realized the rest of the world would
still hate them. Even then, "genocide" sounds like a rather big plan.
You don't need to kill the entire world. You can easily cripple it. So why kill literally everyone? There's no answer given.
And the entire world doesn't have to annihilate Paradis-- they can just take the Founder. Why does Willy call for total war?
More salient, though, is that since the Marleyan Warriors were introduced in full, it was revealed that there have been several characters who consider the problem of hatred and how to solve it
once and for all. Gabi wants to show the world that there are good Eldians, still relying on the world to give them their rights. Pieck recognizes the futility of this especially when they become worthless to Marley after the capture of the Founder, and understands that they need to get their "human rights" by their own hands. Zeke hates his life because his father raised him to be a tool, so he figures it would have been better for no Eldian to have been born at all, especially into a world that hates them and wants them gone. In contrast, Eren desires freedom and will never accept laying down to die after being neutered-- in that case, he's willing to take freedom away from those (i.e. the world) who wish to take it away from him. Minor characters like Sasha's father go on about their "forest" metaphor and how they need to at least save the kids from perpetuating their harmful inclinations.
This objection's been raised in this thread and also in the narrative, but consider the following: for how long would they have to keep this up? In the first place, the plan means that Historia's whole family line becomes breeders because you need to maintain a royal lineage to act as the key to the Founder's powers. But you're
still killing tons of people, and more will rise from the hoi polloi to the military to fight against you. They don't positively value Eldian lives, there's no foothold that exists that allows for them to assert their "right" to life, and they also sit on a coveted resource (iceburst stone). Without also following Zeke's euthanasia plan, they're stuck crippling the militaries of the world in perpetuity... until the rest of the world overcomes the power of the Titans like what was already happening in the war following Marley's loss of the Colossal.
What's even more hilarious is that for everyone in the scouts, NO ONE, NOT ONE gives him an alternative option. They hem and haw and go "But that is wrong Eren." He's literally screaming in their faces to give him something, literally fucking anything, and they don't. They don't give him a single fucking thing. Which means while Erens idea is fucking retarded, everyone is more retarded than Eren because they cannot think of a single alternative idea.
That's... that's the
point. It's not even that they don't give him an alternative option-- it's that they exhaust every option they can think of that could have possibly netted them
lasting peace
without having to make breeders out of Historia's family line. The net result of the diplomacy that they pursued is that they found
one desperate ally on the ropes in their home country that
really wants their resources and nobody else,
not even Eldians from elsewhere, are willing to unite in solidarity for their cause, because a global scapegoat that's largely justified in being a global scapegoat is very convenient for everyone else.
Eren feels like a pawn because nobody takes him fucking seriously and idiotically, constantly disregards him and his warnings. Again, this only works if everyone is a fucking retard. You've got a living weapon and a guy who can see the future says that, barring nothing changes, all of Paradis dies, so help him out. They just lock him up and go "Well, we'll try diplomacy with a society that feeds little girls to dogs and has rape camps and has tortured us for two centuries even though we had nothing to do with anything. Bye."
They lock him up
after the Liberio raid because he was still a soldier and he went AWOL for four years, and also humiliated them by dragging them into a plan by using his secret weapon status as leverage.
"Oh no, Eren killed the children." Give me a fucking break. How many children are Marley responsible for killing, directly and indirectly, in FAR worse and more inhumane ways? He's going to fucking war. You've given him no options. War is obvious and inevitable and civilians are always caught in the middle. Yet everyone keeps shitting on him and giving him no alternatives, which completely kills suspension of disbelief.
That's completely believable. They were tapped for options, which is on them, but how the hell would a military that's thitherto only known war against non-sentient beings and at best have faced combat against a secret service cope with now crushing human children and other civilians into paste?
And its like....wow. This silly anime can do this better than Attack on Titan can (Also don't give me that shit Eren can't do this, he controls fucking causality itself,
Eh? The Attack Titan is special in that it can view memories (however incomplete) in
both directions, rather than merely inherit memories like the other Titans. But that's about it, which means that the extent of the ability is limited to passing messages between inheritors. It also begs the question of what could even be accomplished with that (the lack of presence of future ghosts in Eren's experience possibly means the end of the curse of Ymir overall since inheritance can happen randomly absent succession).
The Founding Titan's abilities are constrained to the subjects of Ymir outside of the creation of constructs. Outside of the subjects of Ymir, it's "only" a superweapon powered by the origin of organic matter.