It's hard to say by just that if it isn't being used. It can be used in ways where you won't be able to see it. Besides that I agree that it's not fair to buy domains just to sell them overpriced. Fortunately for danish .dk domains this is illegal and if one can prove they have better reasons to own the domain and the owner can't prove he is using it, then the domain can be handed over to the new registrant. Unfortunately this isn't the case for other domains. However it is hard to manage, but clearly there's a need for legislation in this area.