They weren't ungrateful, they were bankrupt and unable to show special favor to an idiot who was throwing lavish parties in wartime while America was being flooded with counterfeit Continental dollars to starve out the rebellion's funds.
You can only be a traitor against America. A traitor against the crown makes you a heroic liberator!
How bad can one be?
How willing would other politicians be to accept this? Would there be some sort of coup in order to install or remove Arnold?
In Crossroads of Destiny by H Beam Piper Benedict Arnold became the leader of the American army after Washington was shot dead by a sniper. He went on to become the first President of the USA.
In Britain he was widely detested as a mercenary lacking any honor or scruples, to the point where the British East India Company rejected his application for a position with them on the grounds that he was too generally disliked and controversial. In Canada he moved to a small community and almost immediately began suing people left and right for petty reasons and getting engaged in fierce disputes with neighbors and business partners. He was even accused of burning a warehouse for the insurance money. He won a slander suit for that, but was awarded a meager 20 shillings and a crowd came to burn an effigy of him in front of his house. And that's only his post-war career in part, not even touching on the various scandals and controversies he was involved in on both sides of the conflict.
