It seems that our attitudes toward premarital sex and extramarital sex have an inverse relationship. The more we tolerate sexual activity before marriage, and people “getting it out of their system,” perhaps the less tolerant we become once one makes a commitment to be monogamous. In other words we feel entitled to sexual freedom before marriage because one day it must end.
The percentage of Americans who say adultery is “morally acceptable” has consistently remained below 10 percent. Yet when the French were asked about it in a 2009 poll, 46% said it was morally acceptable. In spite of this difference in attitude, studies have suggested that the actual rate of infidelity in the U.S. is very similar to that in France. So the level of acceptance of adultery is different, but the percentage of those who do have adultery is the same.
If you want to read more look at John Sides’ blog: “Americans Have Become More Opposed to Adultery. Why?”