Many comments here focusing on secrets and problems. But here is another way to look at this:

Environment variables are the "indefinite scope and dynamic extent" variable bindings to make structured programs out of Unix processes. To compare them to a text file is like writing that a program needs no variables because it can read all the values it needs from an input data file when it needs them.

Environment variables are precisely to be used in situation where sub-processes need to be passed information in a way that is not necessarily affecting subsequent calls to that subprocess from another section of a program. Sometime the subprocesses are sequences of nested shells, and sometimes other more complex programs, but the same idea applies.