IMHO people who talk the biggest game ... people who take the most vocal, strident positions ... they don't have a firm inner voice, and inner compass. They are so insecure about who they are inside and what they believe that they need yell out their positions, so they can hear themselves talk.
You know, I have thought about that for a long, long time. I won't go into my ex's back story as its all in my threads and entirely too long. What I have come up with is that I do feel that she is morally against cheating, but due to her past and her own insecurities, she gets caught up and overwhelmed, so-to-speak. She craves attention, and follows it into the very pits of hell.
There are moments in this life when you are so confident in the rightness of your actions, that not even for a second do you consider the option that you might be wrong.