To save the Eldians, Paradis Island, and for his friends to live a long, peaceful life. It's to kill or be killed. This is war. Innocents will be killed either side.
And he chose to prove to the world that the Paradis Island shouldn't be messed with and that the blame can only be on Eren.
Also, he has seen this future and he can't change it. He has no other choice.
dude did you not watch the show/ read the manga? The world was about to wage a war against Paradis. With Marleyan's superior technology, Paradis stood no chance man. The options on the table were - waging war against the rest of the war and euthanization (Zeke's plan). As long as Titans' power remains, Paradis would always be the enemy of the world.
No he could've changed the future like he directed Diana titan into his mother instead of Berthold , he could only distroy the military of all the world but he chooses to kill the entire world instead ! He has done to the world what they wanted to do to paradise !
He said that he tried to change the future several times but the outcome was always the worst. Yeah people skip quite a few lines while reading the manga but did you watch the anime with your eyes closed? He clearly said that while having his last conversation with Armin.
He cant bruh, Eren said so himself that no matter how hard he try to change it, he just cant.
After I watched the last episode it is really clear Eren is only an EVIL KILLER ! his freedom was stolen only by the marly and the politics who gathered to wag a war on paradise so why kill all these innocent people 80% of humanity to prove what ? I really wished he could survive to get punched.