For instance, I would be sad if my phone only gave me one way to turn up the volume. Instead, I like that it gives me 3-4-5 different ways, all useful for different contexts. However, it would also make me sad if it wasn't 'easy' to turn up the volume.
Isn't it the designers job to consider all the different operational contexts and understand all the usage scenarios in all those contexts? And, to make its use 'easy'?
People wouldn't mind if that's what designers did. And it's probably what good designers do - perhaps good design is invisible to most users.
But for examples of what bad designers do see the user interfaces of many graphics manipulation programs over the years. See especially "Kai" and their awful interfaces. Media players are similarly awful.
I don't mind if my one phone gives me 3 ways to do one thing. What I do mind is if that is different for every phone, even from the same manufacturer, and it changes each time they release a new phone.
Huh? What are these "different contexts" for volume on a phone? (There are different things with volume, such as a call vs the ringer, but that's different.)
Another example is encouraging have customization of tool bars. Well designed menus and toolbars don't need to be dragged, dropped, renamed, etc. Allowing this confuses other users of the same software and makes fixing interface problems down the line nearly impossible without undoing all that customization.
Need to edit your user account? Do we need a different interface if you are an admin? Probably not - just a few more fields. Need a file chooser? The same one works for opening word documents as selecting a file for upload.