I find the emotional cheating and the emotional investment of an EA to be more damaging than the PA. Maybe this is just me, in my particular case. My wife was a virgin and young when we married. I was not and had a pretty typical University and High School dating experience. I can understand after 20 years of marriage, a little curiosity. I don't agree or condone cheating, but I can understand the curiosity and what was going on in my wife's head. It's like a delayed adolescence.
It's the emotional investment that bugs me. Sharing intimacies that should be reserved for your husband/spouse. Talking about MY marriage with a virtual stranger. Sharing secrets. Sharing sex stories. Then lying about it. THAT is what bothers me.