"whacked-out mentality to place a cheating spouse on the same moral tier as a murderer or thief"
Hey, a guy will sacrifice his entire life, and even sacrifice his life, for his own childen. When a woman tells a man that he is the father of another man's child, she *is* stealing from him, and in a particularly despicable and damaging way.
That's one thing a woman can do to a man that a man can't do to a woman...unless it's Gracie Allen, maybe.
I'm not saying it would be right, I'm just saying that it's a different kind of wrong when compared to murder or other serious crimes.
And my observation was more general than the specific case you cite - a spouse who cheats on another spouse deserves to get dumped, but they don't deserve death by stoning.