US Senator John Edwards has admitted to having an extramarital affair while his wife was dying of cancer. However, what is even more indefensible, writes Bill Muehlenberg, is that many people are prepared to justify his behaviour.For millennia, the institution of marriage was viewed as a solemn covenant, involving strong obligations and commitment. Recently, however, many Westerners have come to view marriage as just a mere personal arrangement, which can be treated lightly and dissolved at…