Americans are more cynical than ever about politics, and with ample cause. Witness this week’s denunciations of Pfizer Inc. by politicians for trying to survive competitively under the tax laws these same politicians wrote.

On Monday the New York-based drug giant finally announced its long-mooted merger with Ireland’s Allergan in a roughly $160 billion deal that is the largest tie-up in a record year for corporate deal-making. The merger will, among other things, make it easier for the new Ireland-based Pfizer PLC to bring...