But without whitelisting, I wouldn't know how much of the web is completely broken without cookies, where by "broken" I mean a blank page, or just a little strip of the template. This includes blogs, one-off demos, and other sites that don't require (or even offer) log in or settings of any kind.

I can only conclude that some common frameworks depend on cookies for their own operation, and that in many cases the developers aren't even aware of the "problem".