Yud loves to go on about how the map is not the territory, to the extent that his cult followers think he coined the phrase, but he is remarkably terrible at understanding which is which. Or, to be a little more precise, he is actively uninterested in appreciating that the question of what to file under "map" versus "territory" is one of the big questions that separate the different interpretations of quantum mechanics. He has his desired answer, and he argues for it by assertion.

He's also just ignorant about the math. Stepping back from the details of what he gets wrong, there are bigger-picture problems. For example, he points to a complex number and says that it can't be a probability because it's complex. True, but so what? The Fourier transform of a sequence of real numbers will generally have complex values. Just because one way of expressing information uses complex numbers doesn't mean that every perspective on the problem has to. And, in fact, what he tries to do with two complex numbers — one amplitude for each path in an interferometer — you can actually do with three real numbers. They can even be probabilities, say, the probability of getting the "yes" outcome in each of three yes/no measurements. The quantumness comes in when you consider how the probabilities assigned to the outcomes of different experiments all fit together. If probabilities are, as Yud wants, always part of the "map", and a wavefunction is mathematically equivalent to a set of probabilities satisfying some constraint, then a wavefunction belongs in the "map", too. You can of course argue that some probabilities are "territory"; that's an argument which smart people have been having back and forth for decades. But that's not what Yud does. Instead, through a flavor swirl of malice and incompetence, he ends up being too much a hypocrite to "steelman" the many other narratives about quantum mechanics.

Apparently Eliezer was bullied by a Harry Potter fan forum, to the point that some of the users set up a blog called “Methods of Rationality sucks”.

His reaction was where Sneerclub got its name

It's as if /r/iamverysmart sat down to write it. So clearly it's Eliezer self-inserting himself into a children's book as a Jimmy Neutron wannabe and trying to pass is as a legitimate improvement.