Krugman says it's better to let them all expire than to allow another round of Republican blackmail. We already know how serious they are about "temporary" tax solutions.
Bear in mind that Republicans want to make those tax cuts permanent. They might agree to a two- or three-year extension — but only because they believe that this would set up the conditions for a permanent extension later. And they may well be right: if tax-cut blackmail works now, why shouldn’t it work again later?
America, however, cannot afford to make those cuts permanent. We’re talking about almost $4 trillion in lost revenue just over the next decade; over the next 75 years, the revenue loss would be more than three times the entire projected Social Security shortfall. So giving in to Republican demands would mean risking a major fiscal crisis — a crisis that could be resolved only by making savage cuts in federal spending.