What is wrong with another man appreciating her beauty, or whatever else she has that is attractive? Nothing. But another man wanting her causes obvious problems. For you, her, the other guy, or all of the above, depending on what the result is. I'm not talking about somebody walking down the street, they probably wouldn't even notice that she's married. This is about wishing you had your neighbor's wife. If you honestly think that's ok, never mind. This ethical value is common to almost every culture, but if it shows up in the bible, to you it must be stupid - that is how you appear to think, you take this bias to the point of silliness.