[SPOILER ARLERT: Don't read this if you haven't read the scans and don't want to be spoiled]
I think we can start by saying Isayama is a nationalist and I've heard people say the way he draws Titans is somewhat anti-semitic.
The lesson of this serie also seems a bit reactionary, the fact that "walls work" for example, even if they end up not working so much in the end.
The genocide versus self annihilation aspect is also to be discussed I guess. On the subreddit, you can see many people that are pro Eren, pro destruction of the entire world. I guess if one thing can be said about this series is that there are really no actual good guys, everyone is a killer and all factions suck; whether that's good depiction of politics or not, I couldn't say.
I really don't know what to think about the series tbh. On one hand, I really can't deny the plot is meticulously planned and pretty fucking amazingly written for the most part, and the portrayal of racism and discrimination is horrifyingly close to life. On the other hand though, the fanbase is a fash-infested shithole, and Isayama has said some really weird shit regarding Japanese imperialism. From what I got, the manga itself seems to condemn nationalism and fascism, albeit in a very morally gray manner. At first, it tricks you into supporting it with the really basic conflict of humanity vs monsters-- us vs them. After the basement though, once it becomes clear things aren't that simple, it shows you the disgusting consequences that line of thinking leads to-- literally the apocalypse. Ofc though, this flies right over the head of the people who read the series for wow cool titan, and now we got a majority of the fanbase being hardcore Eren stans and shitting up every discussion.
Though it does seem to go back and forth with the "Faascism Works!" to "Fascism is Bad!" enough to give one whiplash, I just think about the original titan (jewish) girl's deal with the devil and the confusion lifts.