Brimic, you make one false assumption there
Emphasis mine
Actually, I've seen the cheater get just as upset as the victim. You're assuming logic, which has no place when discussing emotional response.
Yup - not QUITE parallel, as we weren't married (or even engaged), and no violence was committed or even threatened by either side. Nevertheless, when I was in the Navy, my long-time, long-distance girlfriend started seeing someone else back home one spring. I, being young and stupid, failed to put 2 and 2 together and come up with 4 until a call to her one day led to yet another connection with her mom instead. Mom, who made no bones about the fact that I was her preferred candidate for son-in-law, let me know that Georgia was off in New Braunfels visiting prospective in-laws. Both of us knew that I had no family in that town, so the facts were made plain in about the kindest manner possible. Needless to say, I was angry. Wrote a letter to her to express my opinion of the matter - actually I wrote two, but I kept the one I referred to as "the volcano" and sent "the glacier". Called back a week or two later to see if it had been received, talked to her mom again, who told me that Georgia had virtually exploded in fury. Not over anything I'd said being unjust or undeserved - rather, that she'd been caught, that her mom had told me the truth. Georgia got another note after that, commenting on the lack of respect she'd shown me and her mother and that if she had any further issues with my being told the truth, she could address them directly to me. I didn't hear from her until 7-8 years after that, when she was apparently unhappy in her marriage (to a guy her mom described in passing once as being a lot like me, actually) and just might have been looking for ... something. Naturally, I mentioned to her that while I'd managed to forgive, it would be a cold day in hell before I'd forget, and contact trailed off.
I'll admit to twisting the knife a little in retaliation by sending her an invitation to my wedding several years later...
Anyways, long story short, being found out can induce anger in the cheater as well as the the one being cheated on. They lose the extra sex, or the emotional connection, or whatever it was they used as justification to cheat, and/or lose the "safety net". They're mad at losing a good thing. It's entirely possible that someone might get mad enough to consider or attempt murder over it.