I mentioned this in a post way back, but Eren's turning into the bad guy was a completely foreseeable path, and anyone who tries to say otherwise really hasn't been following the series.
I know I harp on this a lot, but Eren willingly, and brutally killing two grown men at the age of eight is a
huge deal, and now with everything else going on, I'm actually starting to think that it was foreshadowing. Yes, I know the two men were murderous sex-traffickers, but the point still stands. This was an eight year old boy, and yes, I know it's an anime, but really think about this for a minute.
An eight year old boy, with no known prior trauma, or negative influences before hand (I'll get to the PATHs thing in a second)
willingly, calculatingly, and savagely stabbed two grown to death all whilst screaming bloody murder about how "they were a disease" and "had to die".
That is not normal, and even if you take into account that future!Eren used the PATHs system to "influence" his younger self to do it, that still doesn't account for how disturbingly eager, and willing kid!Eren was to kill someone.
I mean, fucking look at 'im.
That, in addition to being unintentionally really funny due to Bryce Papenbrooke's voice cracking during some of the screams, and the whole scenario being just ridiculous, is horrifying. I'm mean, I used to think it was just to be edgy, and part of me still thinks it is, but if I had to give Isayama the benefit of the doubt, I think this was foreshadowing to show just how utterly fucked up Eren was, and how much worse he'd become.
This scene is why I hate when the fandom babies, and coddles Eren. He's not innocent, he doesn't need to be protected, (at least not in the way the fandom thinks), he's not an angel, he's literally psychotic. He's literally always been like this. He's always been a murderous batshit insane lunatic with an outrageous bloodlust.
To get back to the point, I think this scene definitively proves that the possibility of Eren turning out like this was always on the able. Crazy, murderous child becomes crazy genocidal adult. Fucking hell, kid!Eren even spouts the same black-and-white bullshit adult!Eren does, albeit in a much more manic, and unhinged way. It makes sense.
...what doesn't make sense is how what basically amounts to time travel, and Nazis had to fit into this for this ending to happen. That's why, in addition to a fuck ton of other factors, I'm mad about how things have turned out. Isayama had a really unique spin on the the "He Who Fights Monsters" trope, and he managed to fuck it up in ways I didn't even think was possible.
tl;dr;-kid!Eren's disturbing, hilarious, insane, and over-the-top murder of two grown men might've actually been foreshadowing for his current genocidal behavior, and Isayama could've actually had a really cool, and unique rendition of the "He Who Fights Monsters" trope if he hadn't been such a fucking sped.