The same is true for programs that are being invoked. The program only knows relative to its own purpose, and the same is again true for libraries. I don’t see the difference, other than, as already mentioned, the mechanism of program vs. library invocation.

Consider a Smalltalk-like system, or something like TCL, that doesn’t distinguish between programs and libraries regarding invocation mechanism. How would you handle logging in that case?

Okay, but…most programs are written in Python or Rust or something, where invoking library functions is a lot safer, more ergonomic, more performant, and more common than spawning a subprocess and executing a program in it. Like you can’t really ignore the human expectations and conventions that are brought to bear when your code is run (the accommodation of which is arguably most of the purpose of programming languages).

When you publish a library, people are going to use it more liberally and in a wider range of contexts (which are therefore harder to predict, including whether a given violation requires human intervention)

The purpose of a program and of a library is different and intent of the authors of the code is usually clear enough to make the distinction in context. Small composable programs aren’t interesting case here, they shouldn’t be verbose anyway even to justify multiple logging levels (it’s probably just set to on/off using a command line argument).

The mechanism of invocation is important. Most programs allow you to set the logging verbosity at invocation. Libraries may provide an interface to do so but their entry points tend to be more numerous.