Just as easy maybe, but fundamentally incorrect. Its mechanism of action is killing people -- choosing to believe the claim that killing those people will save lives alters neither the purpose nor MO of the tool.
I don't see anything in the page you linked that would qualify him as a "left-wing economist". Neither supporting an openly capitalist political party nor providing theoretical underpinnings for financial deregulation qualify as "leftism".
Re: your last paragraph, it seems to me that the question of "who wields power" will always have material priority -- one of the benefits of power is deciding what is and isn't a "mistake". Look at climate change -- no amount of scientific consensus or popular belief-that-it-is-a-mistake has succeeded in constraining those people whose activities are driving it (I'm speaking not just of DJT's recent escapades in pulling the US from the Paris deal, but the insufficiency of Paris itself). This is power. No amount of problem-identifying/solving has (or will) convince the captains of industry that maintaining their current economic growth targets is less preferable than making vast swaths of the earth less hospitable to life.
It's possible -- I'm not a regular reader of his blog, and thus might be missing stylistic cues, or other occluded methods of admitting a failing. The only thing I read him admit to is that he's less sure of himself than before. Likewise, "Right now I think conflict theory is probably a less helpful way of viewing the world in general than mistake theory" doesn't quite express the idea that "these two theories actually address vastly differing questions that I and the rest of 'respectable' society have been conditioned to conflate". (edit) To clarify: how to obtain power (conflict theory) vs how to effectively wield power (mistake theory)
When I use a word,” Humpty Dumpty said, in rather a scornful tone, “it means just what I choose it to mean—neither more nor less.” “The question is,” said Alice, “whether you can make words mean so many different things.” “The question is,” said Humpty Dumpty, “which is to be master—that's all.”
What this guy's analysis fails to account for is that power matters, smart people coming up with solutions for "mistakes" (whether "hard" or "easy") is necessary, but not sufficient. The question is, and has only ever been, which is to be master -- who has the power?
> Before we talk about Harvard grads destroying the eocnomy, lets talk about making it less and less likely for 75% of the people imprisoned to ever be able to contribute to society once they are released.