Preferences aside, I don't see why displaying full URL can't be an option. Saying that 'Most users won't understand it' or just insisting that it's just better for you even if you don't think so right now is a bit condescending to the user.
Arguing why someone else doesn't need the full URL or why someone else shouldn't need it doesn't make any sense.
Opera could make it hide by default but have an option for those who want to see the whole thing. Even if Opera feels strongly for some reason that a whole URL shouldn't be shown, they could state their reasons on the settings page but still offer the option to people if they want to otherwise.