Comment 5 for bug 746625

And i don't know what APT should make different here. I mean, we can't read the file, so we can't know all sources, so the Cache will be incomplete, so the solution will be incomplete - if we found any. But most likely we will "just" miss important security updates or alike.

So, if we have such a problem, why we shouldn't be allowed to error out instead of pretending that everything is okay?

That setting a sources.list(.d) file as non-readable isn't very useful said already Julian, so you might better of asking the program(s) which created these files to stop making them non-readable…

Sidenote: If it's non-readable because a password is written in it directly they should having a look at https certificates or the netrc-like config file for user-credentials instead…