Among bankers these days, big is beautiful. In the largest combination of two U.S. banks ever, Chemical Banking last week agreed to acquire New York City rival Manufacturers Hanover in a $2.3 billion stock swap. The merger of the two huge but weak Goliaths, both burdened by hefty portfolios of ailing loans, will create a megabank with assets of $137 billion, second in size among U.S. banks only to New York's Citicorp. Moreover, the deal is likely to prompt a new wave of mergers across the country as other big banks struggle to remain competitive.
But the merger will inflict sharp...