Just watched attack on titan. Eren Yeager did nothing wrong

Too bad Isayama made Ereh into a retard in Chapter 139 by turning his reasons for doing the Rumbling into "I wanna make my friends look like heroes" and "I dunno".
He couldn't see the future after his death, Marley could have killed his friends right after and his genocide would have been even more meaningless than it already was.

leftists are mentally ill

The amount of turbocucked redditors who thought Eren made a good villain shattered any respect I had for this shitty shonen slop. Now the series wasn't all that great to begin with, but if you're presented with the option of wiping out everyone who wants to genocide you and your entire race wouldn't you want to do it? Because Zeke's plan was literal sterilization of the Eldians, Marley was subjugating them into ghettoes and wiping them out systematically. There's a massive irony in all of it that the civilization that wants to end suffering is the one that inflicts it. Why wouldn't Eren want to cause the Rumbling when his race is getting wiped out? What's the alternative? Laying down and kissing boots like a cuck?

The turbocucked mangaka went off the rails and made some Marvel movie dogshit in the end. SnK fucking sucks.

It kind of had to end like that or it would literally be Turner Diaries: The Anime. Even in the final episodes his friends didn't hate him, they just thought he went too far. Redditors that think he became a villain didn't get the message that was repeated verbatum constantly: "The world is a cruel place. Kill or be killed."
But yeah I couldn't care less when they tried to make me feel for the marlians. They literally subjected the island to a century of terror while letting the Eldians believe they where the last of humanity.

It kind of had to end like that or it would literally be Turner Diaries: The Anime.

Would've been much better than what ended up happening. The mangaka was just too pussified to see that it was the natural conclusion. Most discerning members of your audience are not going to be satisfied with all of the most beloved characters in the series just giving up and celebrating SnK's version of the holocaust. What's even more retarded is that they tried making Floch seem like a pathetic bad guy when in reality he was who we were cheering.

Even in the final episodes his friends didn't hate him, they just thought he went too far

Which is retarded. There are no geneva conventions in this universe. It's a dog eat dog world as you said, and these characters have no reason to feel sorrow or sympathy for characters who kill them off and openly root for their deaths. Sasha dies and then suddenly all of our remaining cast decide to just forgive Gabi, what a tortured soul right? It's like all of a sudden these characters turned into modern American liberals when the plot wanted them to go against their best friend and the protagonist of the story. In an actual situation like that they would realistically be out for blood. It's the natural order of things.

they just thought he went too far

And this is bad writing because they grew up in a medieval fascist dictatorship besieged by giant cannibals so their modern liberal mindset post-timeskip is literally an asspull