The crux of sharing spectrum (as any down to earth shared whitespace proponent will tell you) has to do with the rules the cognitive radios use. Liken these to rules of the road or right of way. Traffic on the roads and freeways works (for the most part) because of a common understanding of the rules that govern right of way. These rules are determined by the government (in some cases better than others, try figuring out when you can do a u-turn in a given city).
The point is that while in theory, sharing unused white space is great, the devil is in how you share it. Without rules and guidelines defining this sharing of whitespace will simply be a property grab.
Think radios positioned to transmit constantly when they don't have actual network traffic. Think about radios that start bombing unused whitespace to claim it for a telco as soon as it goes out of use. Defining the rules of the road is a good thing. The EU may do a bad job of this, but it still needs to be done before that grand idea of free spectrum can even begin to have a hope of being realized.