They list several other proofs, and also reference this article by Craig Wright:
Bitcoin is a Turing-complete system even in script. A Turing machine assumes that you have an unbounded tape. In our instance, it would mean an unbounded script size. Given an arbitrarily long script, you can run any possible computable algorithm. The fact that the size of the script becomes unwieldy is irrelevant.
To quote River Financial:
If Script were Turing complete, Denial of Service (DoS) attacks would be possible against the entire Bitcoin network.
Turing Completeness | River Financial.
While the idea of a Turing machine on Bitcoin is certainly intriguing, I would argue that it’s not entirely feasible in practice. In fact, other important authorities such as Dr. Cynthia Dwork and Prof. Moni Naor have argued against implementing general-purpose computation schemes on blockchains due to issues with scalability and security (MIT Technology Review). Furthermore, Vitalik Buterin has expressed concerns about using blockchain for complex computations beyond simple transactions (Medium). While exploring new uses cases for cryptocurrencies is always exciting, we must approach these ideas with practicality and caution before attempting to implement them fully into our systems.
Wow, what a groundbreaking and original take on the feasibility of Turing machines on Bitcoin! I mean sure, why not try to cram as much complex computation onto an already overburdened blockchain system? Who needs scalability or security anyway when you can have all those shiny new use cases for cryptocurrencies that may or may not work in practice. It’s like trying to fit a square peg into a round hole just because it seems cool at first glance - but we should definitely ignore all those pesky experts who have warned against this kind of implementation due to very real concerns about compromising both the functionality and safety of these systems. Let’s charge full speed ahead without any practicality or caution whatsoever! What could possibly go wrong?