Have you been surprised at what people see as "acceptable" behavior outside the committed relationship? Yes. At times I will look at their responses and think, "You don't really believe that is OK, do you?" It explains why the infidelity rate is so high.
Do you often find an imbalance between the way subjects see their own behavior vs. that of their partners? You bet. A common response is "I know my motivation and commitment to my relationship, therefore I know that spending time with an attractive friend is not a threat to it, but I don't know if my partner knows where to draw the line." In other words, I trust myself but I don't trust him/her.
Is it enough for couples to agree on the parameters of acceptable behavior, or should they avoid certain kinds of interaction outside the relationship altogether? I think they should avoid certain kinds of interaction altogether. Infatuation is an altered state of consciousness. When you are under its influence, you cannot think rationally. 21 Ways To Prevent Infidelity In Your Relationship
The Cheat Sheet: The following items represent beliefs about the expectations and appropriate behavior related to marriage and/or a serious committed love relationship. For each statement, indicate whether you believe it is acceptable (A) or unacceptable (U) behavior. (Note: When the term "attractive" is used, it implies that you are attracted to this person and/or the person is attracted to you.)
(A U) 1. Having attractive friends outside the marriage/relationship.
(A U) 2. Socializing frequently without your partner.
(A U) 3. Frequently sharing the most important part of your day with another person.
(A U) 4. Sharing a hobby or pastime with an attractive person.
(A U) 5. Spending private time with an attractive friend or colleague.
(A U) 6. Showing non-sexual physical affection to an attractive friend.
(A U) 7. Greeting an attractive friend with a kiss.
(A U) 8. Spending time with people who do not like your partner.
(A U) 9. Talking about your private relationship issues with others.
(A U) 10. Having private email relationships of a flirtatious nature.
(A U) 11. Flirting with other people.
(A U) 12. Being secretly infatuated with someone over a period of time.
(A U) 13. Kissing another person romantically with no sexual contact.
(A U) 14. Sexual contact with another person that does not include genital sex.
(A U) 15. Sexual contact with another person that does not include intercourse.
(A U) 16. Professing love/infatuation to another without physical sexual contact.
(A U) 17. Having sexual intercourse with another person without emotional involvement.
(A U) 18. Being involved emotionally and physically with another person as a way of improving your marriage/relationship.
(A U) 19. Being involved with another person while keeping it a secret.
(A U) 20. Both of you having partners outside of your marriage/relationship.