Originally Posted by polyexplorer
I have a value that it is wrong to take another life. Would I take the life of someone who was about to kill my daughter - of course I would! That is an exceptional case.
I don't lie to people. I am a very honest person. Would I tell a lie in WWII days if I was harboring a Jew in my house in order to protect them from Nazi Germany? You bet I would! That is an exceptional case.
The problem with these two examples is that the hypothetical you is acting to protect another person from the evil intents of someone else than you. While in cheating, you are committing evil against your partner, and there is no one to protect them from you. Unless that is the hypothetical unattached/openly non-monogamous person whom you are considering starting an affair with, who in this situation has the power to say no, I won't go down that path.