Ahh...a New Democrat whining about a politician that has overturned Blairism in his party, and thus, Third Way Neoliberalism that both factions championed.
Being skeptical about US cultural, economic and financial hegemony is not a mark of lunacy: it's a valid, if arguable, response to the situation in the world. As to Americans being inexperienced at dealing with far-left politicians, the obvious riposte is that Americans have almost no experience at dealing with politicians of any shade of left. Take Obamacare. It's a right-wing solution (by the Heritage Foundation with roots to Nixon) to the problem of healthcare provision, first enacted by Romney, and yet it's somehow a "socialist" aberration. The whole spectrum of US politics is so skewed to the right from the European point of view.
Those who detest Corbyn are really afraid of what he represents, a voice for the average person to have some input into an otherwise rigged process. When the wealthy can't buy what they want regardless of what it is, they start making silly arguments like those of the writer.