We need to decide on a policy to log errors. Or rather, how how we will allow our users to control that policy.

First A rant

I think libraries should not log, that is a decision for the application, how, where, and what to log.
Libraries should maybe have a hook that the application can set, and maybe can chose to print to stderr by default, as long as the hook can be changed. But they should not force applications to use one form of logging or another.

Back to the original programming

There are some events, such as servers returning incorrect data, that should result in either exceptions, or a log message. Those that can be safely ignored probably are log messages, but the application should have hooks to control them.