Today's Strict immigration rules may threaten Japan's future (by Chico Harlan, Washington Post, July 28, 2010) is essentially the same as a New York Times version almost exactly five years ago, which Jared Taylor debunked for us here. The fundamental economic point is that labor is only a small component of the factors of production: technology matters far more.

Japan's population may or may not decline (demographic projections are notoriously uncertain) but declining populations are not neccessarily bad. Here's Wikpedia (July 28 2010) on the economic consequences of the Black Death:

In many ways the Black Death and its aftermath improved the situation of surviving peasants, notably by the end of the 15th century. In Western Europe, labourers gained more power and were more in demand because of the shortage of labour. In gaining more power, workers following the Black Death often moved away from annual contracts in favour of taking on successive temporary jobs that offered higher wages