Five thousand women—many from Lima’s top society—heeded the call, parading past the presidential palace and the cathedral and chanting hymns. The demonstration persuaded Peru’s church ...

These are are the reasons more women are turning their back on the idea of a traditional marriage.

This would bring Peru in line with other nations in South America, including Argentina, Uruguay, Brazil and Colombia, which have legalized gay marriage in recent years.

Modern women are pushing back, asking why they should commit to a role that demands so much and offers little in return. Marriage, for some, has become more of a negotiation than a celebration.

A common narrative has it that commitment and motherhood make women unhappy. New data suggest the opposite is true.

It is sometimes said that marriage does not increase — and perhaps, that it decreases — women’s happiness. But is that true?