I think the biggest problem with Pluto is that it doesn't have a coherent politic. Having an incoherent politic isn't normally a death knell for manga but you can't do that in an intensely political manga with a war in the Middle East and weapons of mass destruction.
Pluto, by the way, ends up making the Middle Eastern country (Persia, aka Iran) actually guilty of making the weapon of mass destruction. Here I'm going to conflate Iraq and Iran a little, because Pluto is ostensibly about Iran/Persia but the real life invasion was against Iraq. Why was Iraq invaded? Because Bush and his goons said there were WMDs. Why was Persia invaded? Because "Thracia" suspects it of building a WMD. In real life Iraq famously didn't have WMDs! In Pluto, Persia did! The big reveal is that a huge bomb was buried under the sand. Lies! Damned lies. How big of a hawk do you have to be to fantasize about Iraq actually having WMDs and thus deserved its destruction?
You then have these 7 strongest robots some of whom actually killed humans and participated in the destruction of the Middle East, and we're supposed to feel sorry for them? It's absurd.
To which Pluto says: Nothing will be born from hatred. I.e., I know I destroyed your country and killed everyone but let bygones be bygones. Well, convenient for the US then, I mean, for Thracia to say. "Nothing will be born from hatred" is bad because it is a lesson in a children's book. It doesn't say anything about the underlying conflict. There was in fact no sense of an underlying conflict except that a war spawned from thin air for the usual purposes of "restoring democracy" with vague nefarious goals. No, conflicts are fought over resources, land, oil, water. They're fought to sustain war machines for countries whose economy relies on the production and sale of weapons. Pluto is clever enough to realize that "restoring democracy" is a lie but it still doesn't know the truth. If offers no truth. Hatred is not why we fight. It doesn't understand why we fight.
Then there's the part about robot equality too. Robot equality has always been made an analogy of the struggle against racism, but it does not help that there is such backlash against AI now. Now that AI has "arrived," we can see all too well how completely inadequate AI is, how a human mind is never going to be replicated by programming, how this particular strain of science fiction had failed to anticipate how AI would change the world. AI is changing the world, but not in the way that Pluto anticipated. There is visceral hatred against AIs, but it's all deserved. And the analogy to racism now feels cheap, presumptuous, deceiving. The reach for the analogy to racism is furthermore perfunctory and unearned because racism doesn't really figure into the larger story at all, even though in the real world the Iraq war produced insane levels of racism, but of course the real world racism was against people in the Middle East and not an abstracted robot population.
Crazy how much a manga has aged in twenty years. Pluto was published in 2003. The US invaded Iraq in 2003.
How was Urasawa to know that there was no weapon of mass destruction? But doesn't it seem silly now that they insisted a nuclear bomb sat buried underneath the sand?
Isn't it a little sickening that someone whose entire family was destroyed is told that "nothing will be born from hatred"? Pluto wants to have its cake and eat it too. It wants a tidy, heroic story and yet to also toy with international politics. It wants pathos for people on both sides of the war, the aggressors and the trampled upon. Who is worse? Insurgents who kill people they hate, or soldiers who kill strangers?
Look, no matter what your stance on the Iraq war is I think the vapidity of "nothing will be born from hatred" will annoy you. For me, I'm a leftie, so I recall that classic Alexander Cockburn habit of asking people if their hate is pure. Yes, hate can be justified, desirable, and good. Should war crime perpetrators not be hated? When they kill a million people in Iraq what kind of person would I be if I don't hate every single one of Bush, Cheney and them? I hate them, I hate them, I hate them. I don't know, maybe I'm stupid sensitive to the Iraq war since it happened at a formative time of my life, and Pluto didn't sign up to make a statement about the most defining conflict of the twenty-first century. But why invoke the most defining conflict of the twenty-first century if you didn't have a damn good statement to make about it? Fullmetal Alchemist certainly was better prepared for having started publication in the same year. There is no excuse for having a vapid, wishy-washy moral about Iraq.