There isn't a "national interest". Taking sides in the Middle East’s political and religious civil wars has undercut our credibility. Our role as collaborator in the Palestinian oppression is a major source of anti-Americanism in the Muslim world.
Employees are now becoming variable costs of doing business—depending on ups and downs in demand that may change hour by hour, possibly minute by minute.
Grexit costs would be very serious not only for Greece but for the entire Eurozone and beyond, but unilateral withdrawal from the whole of the European Union rather than simply the Eurozone would make more sense.
The typical worker has seen almost none of the gains from economic growth over the last four decades. But tax deduction gives billions of dollars every year to some of the richest people in the country for no reason whatsoever.