In theory you could just not use the app. Also, tell the app owner why you're not using it. However, I'd say that there's generally no consistently way I've seen that FB gives you to give feedback to app owners - certainly ones which you're not actually a user of the app too.
If enough people did that (or started to from now on) the demands for extended app privileges might drop.
If enough people did that (or started to from now on) the demands for extended app privileges might drop.