the problem is really that it is too functional.
can think of it in the following way:
i could say some simple idea in a very fancy and complicated language that'd make the idea not only impossible to understand, but to not even contain enough information to explain itself.
for a mathematical example, whenever i use arithmetic to express my ideas, i give up the way to answer all questions, due to godel's incompleteness theorem.
it is impolite to say something in an undecidable language (turing complete) if one can say it in a decidable language (which must be restricted comparing to turing complete languages) and by that the listeners can in principle have answers to all relevant questions.
this has far reaching consequences. for an example about turing completeness' undecidablity and security, cf this lecture https://www.youtube.com/watch?v=3kEfedtQVOY