Politics of the Era
By playing up the conflict between the Butcher's Natives, and Vallon, it threw off the real politics going on in the Civil War era. New York City, but especially Tammany Hall, were essentially like a fifth column for the Confederate states.
The Republican platform of the day was tariffs and protectionist isolationism, with government subsidies going to textile mills in New England and railroads. The Democrat platform was free trade with Europe, and the gold standard. The shipping industry that dominated New York was not favorable to the Civil War, as it strained relationships with inter and intra national shipping.
Tilden, Seymour, Grover Cleveland, Parker were all New York Democrats that carried the South in the post Civil War years.
The conflict in New York, that lead to the draft riots, was the fact that Irish new citizens, were being drafted by people "above" them to free people they saw as "below" them. A class war in 2 directions.
The Butcher's character muddies the waters of the accurate politics of the 1860s. Boss Tweed and his racist, populist Irish base were fighting against progressive wealthy textile industrialists, who supported the abolition of slavery.
Not Irish fighting against knife-throwing reactionary "natives". The Know Nothings were dissolved in 1860.