Should George W Bush be put on trial for Iraq?

[Since I'm the mad scientist proclaimed by myself]

Iraq unlike Ukraine was a totalitarian dictatorship.

Unprovoked aggression doesn't become magically okay if the country targeted is a dictatorship.

Dictatorships have no legitimacy and don't deserve to be respected. The problem with the Iraq war was the consequences of it(though I've heard some arguments that Iraq has improved enough to make the war ultimately worth it, at least for Iraq itself. I'm not sure what I think about that, but it's not absurd on its face.

[Since I'm the mad scientist proclaimed by myself]

A country is more than its government. And if there are no democratic institutions, why is a dictatorship necessarily an "illegitimate" government?

Governments in general don't inherently deserve respect. Dictatorships are defined by brutal repression and cruelty towards the masses done so that the elites on top can keep their lavish lifestyles and unchecked power (and "brutal repression and cruelty" in this case is far worse than anything we see in the US). I don't see why a government defined by the oppression of the populace deserves to be respected and protected. What is your justification for that?

By your logic, was no 15th century government legitimate because none were democratic by today's standards?

No 15th century government was inherently deserving of sovereignty, yes.