The problem isn't that there is any state involved, it's that we as programmers must reason about that state.

Evaluating "(1 + 2) * 3" requires some state in the CPU, but I can treat it mentally as just an expression that be reduced down to 9 without me feeling like there's state involved.

The only thing that matters in my opinion is if it affects our ability to _reason_ about it

isn't it minimised if the compiler/OS manages it instead of you?