Don't know why you focus on "good and evil" when it is more down to whether a person sane or insane. When Thanos want to snap away half of lives in the universe so that everyone have better lives. Is he as adorkable as Eren? Is he not a villain? Is he even sane? Give you a hint, they called him the mad Titan. And the problem there is, well, if going by the population curve, it ain't taking that long for any population to double. So I guess Thanos would have snap his finger over and over and over again lol. When weld absolute power, his imagination is so limited to not able to find simple solution to his problem. How about endless resources. Endless renewable energy.
I think people take comfort if Eren was crazy and insane, because then you can blame on PTSD or trauma or whatever. But rational cold calculation, it makes one feel unease. Because we see it before in human's history. Holocaust, genocide, nuclear bomb. I think I actually addressed all of your points in an early post up this thread somewhere. This is nothing more than the thought experiment of Nuclear first strike. I said up thread somewhere that Marco's last word of "talk it out" which haunt Reiner is really powerful.
https://mangahelpers.com/forum/thre...hapter-discussion.3018924/page-5#post-5481817
In Ravages of Time, these two ideas clashes. Sima Yi want a bloodied style rival that of the Red Wedding to end the suffering of war quickly. End the war at any cost. Whereas Zhuge Liang would rather avoid that to preserve morality and values. Even series like Kingdom, where the PROTAGONIST want extermination, and genocide in the name of unification and peace. Of course, history told us, that empire last a meager 15 years. Peace achieved by that sort of meant, may not always work out. And that is the ending of AoT, nothing is certain.
Btw, as a former military member and actually have mental health diagnosis. I don't know how you can think Eren is anything but psychotic. A sane person wouldn't make those choices. lol, the last few weeks, I am start to hear voices in my head especially at night. Thinking about how real it is physiologically, despite the logical part of my brain know that it isn't. Ain't it any different than hearing the voices of God, or seeing imagery that you think must happen. That is pretty crazy. The author only incorporate that element in after he saw the Game of throne episode the Door (or actually the one with the Tower of Joy), where one of the character was able to influenced the past. As far as I know, maybe he had some ideas before that.
*At least you aren't one of those people who think Eren is in the right. Holy cow, I stumble upon a couple of them. And I hope dear God. That they never in the position of power. To be honest, the scope of the story shouldn't have been this big. Once it got to be this big, I don't think anyone could write a satisfy ending.
*IN summary, my disagreement is over whether he is psychotic or not.
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Ever since the Buddha showed up in Record of Ragnarok, I remember the phrase (to me associate with Buddhism) if you don't go to hell, who would? To me, it meant to do the hard thing, and sometimes the morally hard thing. For a Buddhist that came to the famous trolley problem. Do you do nothing, and let 5 people die. Or do you do something and save 5 people, but in the course of that murder an innocent bystander that would not have die if you didn't do anything. The boring Buddhist answer would be throw himself on the track and cause the trolley go off rail saving all 6. But if that isn't an option, "the going to hell part" is being the person to make that morally complicated choice to save another person from the guilt and sin of making that choice. Kill 1 to save 5. And suffered the consequence for that action. But that isn't a A or B situation like Wanda had to face in the last episode of Wandavision. Though with that one, I actually go with harming the majority. I don't think Eren embodied that phrase at all. He killed the majority of the population, leaving the world with potential chaos. Have you see a country after bomb campaign or this case Eren flatten everything. No infrastructure, no law, no order, shortage of resource, extremely high tension.
I am okay with the ambivalent ending that nothing really is solved. Which is preferable between Code Geass and Watchmen. The former said that tactic would work, the latter said that tactic may not work. But in all these cases, it is killing a few to save or bring peace to the majority. In Eren's case, the decision didn't need to happen like that in term of agency or how it happened. It crossed into the dilemma of Wandavision, where I think you are more obligate to the children that you bring into the world and or people that you owed something to over random strangers. In essence, all lives are not equal objectively and subjectively.
But what Eren did make no sense to me. How can he be so sure that it will happen the way he see it, especially those future isn't just necessary just depend on his action. And in the process of doing what he did, he almost killed and could have killed everyone he held dear to. There is no guarantee that he wouldn't. In fact quite a few die to get them to where they were in order to face him.
To be honest, if you applied outside logic. All they have to do is destroyed all those serums, so no one can transformed into titans. And since there is no other physiological trait that separate them with the normal population. Because if there were, then the whole squad couldn't have infiltrate the mainland. And beside, there are countries that totally cool with Eldians anyway. Then just mix in there, and no one can tell. And who know, after many generation of mix breeding, the Eldian gene may just dilute enough to irrelevant. Use the founder titan power to brainwashed the mainland Eldians and erase their hatred. Then there are the 9 titans. Have someone eat up every other titans when they close to dying and have all 9 in one person. And pass it down to an elected or well regarded person of the community. Then keep passing it down to people in their 50 or 60. So that at least they live a full life. Problem solved. Marley wouldn't even be a threat to world peace, because their number one weapon, the titans, are not in their possession this way.
Peace is not permanent, nor is a total just world can be achieve. But there is always meaning to thrive for that regardless.
To be honest, if happened in the real world, anyone with the attack titan, probably just hanged themselves.
and I truly believe it was the best one amongst the ones still ongoing. 
