But in Reality:
Arnold actually did all that stuff. Switching sides, trying to surrender West Point, the whole shebang. But you know what? Considering the circumstances, it's hard to say we blame him.
This shameless display of unmitigated gall, however, is inexcusable.
When you look at pre-treachery Arnold, what you find is an almost comical beacon of good old-fashioned American virtue. After his mother died, he single-handedly supported his sister and suicidally alcoholic father; he enlisted to fight off a French invasion when he was 15; he grew up to be a successful capitalist and family man. If he'd fought a duel against somebody for using "Yankee" as an insult, he would've been the ultimate American. What, he did that? Never mind then.
Then there was his record during the revolution. He planned and led the famous siege of Fort Ticonderoga. Somewhere around here his wife died, but he soldiered on, masterminding the strategic invasion of Quebec, where he held position for weeks despite being cut off from the rest of the army and shot in the leg. He held back the British at Lake Champlain, he was instrumental in the Danbury raid, he was essential to the success of the Battle of Saratoga. If he fell off a bridge and died at this point, there would be a 50-foot tall statue of him in Connecticut, made of platinum and diamonds.
The army must have loved this guy, right? Surely by this stage he was being carried everywhere by a living throne of nubile young women. Wait, instead they repeatedly passed him over for promotion with younger, less experienced men? And other officers tried to take credit for his achievements? And he was investigated by congress on baseless accusations of corruption?
Basically, after all his bravery, sacrifice and bullet holes, America seemed to develop a great passion for kicking Arnold in the gut. It didn't help that at the same time they were creating an alliance with France, the bad guys from Arnold's teenage war adventures. Under those conditions, it's understandable that he'd quit the team.