It seems to me that you entirely miss the sleight of hand the trickster uses.

Utility function is fuzzed (due to how brains work) together with the concept of "functionality" as in "the function of this valve is to shut off water flow" or "function of this AI is to make paperclips". The relevant meaning is function as in mathematical function works on some input, but the concept of functionality just leaks in.

The software is an algorithm that finds values a for which u(w(a)) is maximal where u is 'utility function', w is the world simulator, and a is the action. Note that protecting u accomplishes nothing as w may be altered too. Note also that while the u, w, and a, are related to the real world in our mind and are often described in world terms (e.g. u may be described as number of paperclips), those are mathematical functions, abstractions; and the algorithm is made to abstractly identify a maximum of those functions; it is abstracted from the implementation and the goal is not to put electrons into particular memory location inside the computer (the location which has been abstracted out by the architecture). There is no relation to the reality defined anywhere there. Reality is incidental to the actual goal of existing architectures, and no-one is interested in making it non-incidental; you don't need to let your imagination wild all the way to the robot apocalypse to avoid unnecessary work that breaks down abstractions and would clearly make the software less predictable and/or make the solution search probe for deficiencies in implementation, which clearly serves to accomplish nothing but to find and trigger bugs in the code.