a) What is the point of opening files that will never be written to and
sockets that will never be used? 

A large application might have a great many loggers for debugging which
are off by default, and this means you have to either put up with lots
of empty files being created all the time, or tell everyone that they
need to change the configuration in two places each time they enable or
disable a logger.

Logging config files need to be easy to tweak, even for people who
aren't coders: it should be quick and obvious how to enable or disable a
logger.

b) I don't see why making those sections optional would break backward
compatibility. It would be easy to just silently ignore them if they
were present (or call today's code that uses them). 

I'm aware that "qualname" isn't always the same as the section name. My
point is that it should not be *compulsory*, not that it shouldn't
exist. It has an obvious default value so it's wrong to fail with a
python stack if it isn't present.

c) I know there are other packages out there. I've been using log4py for
years, which is now abandoned. But Python now has an official way to do
logging and I think it should be more user-friendly for simple usage
than it is. I can write my own config file format without too much
difficulty but it seems a shame if everyone ends up doing this.

(The one you linked to seemed to have wider ambitions than logging and
its format seemed even more unwieldy. Curly braces in Python?!)