Even the example you've taken for WWII, UK and US weren't the aggressor. The war already at their door for British, so they had a little choice in it. Similarly for US they knew, if they don't do something early enough, they could end up being a victim or suffer from it eventually. So they had to support Britain in the war.
There are many wars where multiple sides are belligerent. There are wars where a side manages to profit or benefit from a conflict without appearing as a belligerent. And there are wars where it's not clear who the beligerent is.
In the French Revolutionary wars, France appears as the aggressor, as they declared war first. But they declared war as a pre-emptive to gain advantage in a conflict with Austria over Bourbon restoration that they felt sure would come. And judging by contemporary history (the partitions of Poland, the Hungarian rebellion, the Revolutions of 1848, etc), they were probably right.
There is the Franco-Prussian war, a war which was essentially desired by both sides.
Most civil wars rarely have a clear beligerent side with slow escalation of violence by multiple parties.
We are deep into the era of nationalistic propaganda so we are used to conceiving of wars as clear conflicts between two cohesive political units: one the aggressor and one the defender. But that is a concpetion mostly born out of our experiences in the 20th century and even then it is highly biased by the popular narrative of WWII.
And to that matter, some of what brought the U.S. into the orbit of WWII was a lower key version of the kind of foreign policies of that earlier era. Disrupting Japanese interests in Asia was very much about economic benefit and power balance in the mode of realpolitik.
And in the end, the Roosevelt administration remains unique in American history for how hard it pushed against colonialism. Truman was much more aligned with British interests in this way than FDR. So while the war is justified in the name of stopping two monstrous regimes, its precursors and its aftermath do carry a fair amount of the same taint that Butler thoroughly observed in his time.