ID cards and identity

The Home Office seems hell-bent on making us all carry identity cards, despite the apparent scepticism of the police about their likely benefits in detecting or deterring crime (very little benefit fraud is based on false identity, and real crooks will quickly find profitable ways of manufacturing plausible forgeries of the things) and despite the strenuous opposition of the civil liberties lobby.  Elements of possible smart ID cards are to be "trialled" (or tried out, as humans prefer to say) in a ‘small market town’ shortly.  The Cabinet is said to be lukewarm and even Mr Blair is said to be unconvinced, but no doubt Mr Blunkett, ever vigilant for opportunities to extend state power over the individual, will get his way in the end.  One of the purposes of ID cards, according to the Home Office, is that they would provide a way of stopping people using two or more identities.  But why should such a relatively harmless practice be "stopped" by the State?  Provided that assuming a second identity isn’t done to obtain money under false pretences or involve obstructing the course of justice, or entail any other illegal activity, why shouldn’t Mr Smith become Mr Jones while he is spending a pleasant weekend with "Mrs Jones" in Brighton, or visiting his second, undeclared family in Malaga?  Indeed, why shouldn’t he become Mr FitzSimmons now and then to escape the boredom of being Mr Smith, thus enabling him to enjoy the luxury and liberty of a wholly different and more flamboyant personality for a while?  Because, evidently, it would be too untidy for the Home Office, who like to know not only where we all are (by putting little trackers in our cars and wheel-chairs, their latest jolly idea), but also who we are at any given time.