I think the concept is best seen as an instrument of conflict between competing sources of power. In particular, the meaning of 'rights' at a given time represents the ideological position at that time on the issue of state-versus-individual. When we had absolutism, talk was of the absolute rights of the state (monarch). As civil liberties developed during eighteenth and nineteenth centuries, the language of 'rights' was increasingly used to express the idea that each individual has their own territory or area of sovereignty.
In the twentieth century, the concept swung back towards expressing the claims of the collective (in effect, the state) on individuals. In some cases, spurious terms such as 'Volk' or 'proletariat' were used to denote the collective.
We see this swing continuing today under Blairism, a philosophy which — for all the criticism directed at it by now from every corner — can readily be interpreted as an ideal expression of the prevailing Zeitgeist. The idea that the individual has a claim to be left alone by society (e.g. to smoke, or to eat supposedly unhealthy foods) has become, it appears, outmoded.
Other takes:
Stumbling & Mumbling: "Rights, if they are to be meaningful, are not merely something that governments grant to people through legislation. They have moral force ..."
Westminster Wisdom: "Often it strikes me that most who use the term and ferociously argue about it have different definitions of the word, right, but because no one defines that term, persist in thinking that they should agree and can't really work out why they do disagree."
Chris Dillow (commenting on WW): "What you say of rights is true of other categories - justice, liberty and efficiency. Incoherence afflicts almost all popular thinking about moral and political philosophy. ... MacIntyre said it was because we have inherited multiple, conflicting traditions - a sociological fact as much as a philosophical one."