[PaulDavisThe1st]

If env vars don't exist, that makes it much harder (and more likely impossible) for users to modify library/application behavior at run time.

I agree with you that it would be much better if, when libA needs to set behavio Foo in libB, it called libB:setBehavior (Foo) rather than setenv ("LibBehavior", "Foo")

But let's not throw the baby out with the bathwater.