Bill Gates calls for infinite visas to fill the 'critical shortage' of high tech workers in US. Greg Mankiw's blog post has on this has attracted the expected spectrum of opinions on this issue.
Unfortunately the spectrum does not go wide enough to cover complete 'freedom of movement' for all people across national boundaries. While restrictions on movement of capital, goods, knowledge are rapidly reducing, existing barriers on free flow of labor does retard our march towards the overall goal of "global economic integration and interdependence" for everyone's benefit.
Clearly labor markets are getting integrated using Interent ( where services can be provided from a remote location ) and the trend towards temporary and short term labor mobility replacing permanent migration.
All this means countries that choose to isolate themselves from these integrated labor markets should be ready to pay a price for that choice