MW is not just a goofy interpretation. It turns a good scientific theory into something that is contrary to all of science. It eliminates the ability to make predictions.
Even today, almost 90 years later, the anti-quantum zealots who are still around – depending on the degree of their stupidity – argue that quantum mechanics is either wrong or incomplete. The typical complaint that "quantum mechanics isn't complete" is formulated as follows:That's right. And if you support MW, you abandoning the primary purpose of science. (I am avoiding the word "interpretation", because it is not really an interpretation. Calling it an interpretation is part of the hoax.)But the Copenhagen Interpretation fails to tell us what is really going on before we look.Well, in reality, quantum mechanics tells us everything that is happening before the observation: nothing that could be considered a fact is happening before (or in the absence of) an observation! It is an answer. You may dislike it but it's a lie to say that you weren't given an answer!
Needless to say, the statements are upside down. The Copenhagen Interpretation provides us with a definition which questions are physically meaningful; and with the method to determine the answers to these questions (which must be probabilistic and the axiomatic framework clearly and unambiguously says that no "unambiguous" predictions of the phenomena are possible in general).
Instead, it's the anti-quantum "interpretations" of quantum mechanics such as the Many Worlds Interpretation that are incomplete becausetheir axioms just don't allow you to determine what you should do if you want to calculate the probability of an outcome of an observation.
In particular, the Many Worlds Interpretation denies that there's any collapse following Born's rule (an axiom) but it is rather obvious that when you omit this only link between quantum mechanics and probabilities, the Many Worlds paradigm will become unable to actually predict these probabilities. You created a hole – (because the building block looked ideologically heretical to him) someone has removed something that was needed (in the Copenhagen paradigm) to complete the argumentation that normally ends with the probabilistic prediction.
This is an actually valid complaint because the primary purpose of science is to explain and predict the results of phenomena.
Motl doesn't name names in this post, but an example is Sean M. Carroll. Motl probably has more distinguished physicists in mind, and doesn't want to embarrass them.
Belief in MW is a belief so goofy as to discredit whatever other opinions they might have. It is like believing in the Flat Earth, or that the Moon landings were faked.