the other woman gets blamed in a cheating situation more vehemently not because she is more at fault, but because the community of the man can't hold her accountable.
think about it. if a man cheats, everyone he knows will know. everyone can have an opinion, and as such, he can work to make amends. The women, though, she usually disappears (usually not being a person in that community). she was invisible in the relationship, sometimes the community doesn't even know her identity, and then she disappears into the ether.
Thus, the natural need that we have to create amends (our internal communal needs) are not met. She has not been held accountable. As such, the vehemence towards her stays the same or increases because there was no opportunity to rightly vent the feelings and frustrations to her and have her make amends.
I've actually seen it in both situations.
In one situation, where he cheated (instigated) and she agreed (knowing he was married according to him), when his wife found out, she was very upset. He refused to say who the other woman was. Their marriage did survive (with counseling, work, etc), but she still holds on to a LOT of vitriol toward the woman because she was never able to confront.
In another situation, where he cheated (instigated) and she agreed (knowing he was married because both people attended the same church), when his wife found out, she was very upset. The whole community was upset, and she was able to confront the "other woman" -- and did so both publically and privately. The marriage survived, they all still attend the same church, and even though those two women are not friends, they can work together on committees well enough and so on. And, no one is holding any particular, intense vitriol. Instead, there's more of a "whatever" sort of feeling between the women, and while there's still a scar for the husband/wife to contend with, the reality is that the whole thing is much more peaceful.
In my own case, my husband didn't cheat, but there was a woman who had designs on him. She was also married, and they'd met at a conference. I pointed out to my husband (when he would share her emails with me) that she was giving him the 'full court press' (a basketball reference of offensive positioning, btw). she was making it very clear that she wanted him. He was like "no, no, she's just being funny." or some such. He's a bit dense about these things.
Later, he went out to some meetings, and she had invited him to stay with her. I agreed, because he was like "it's free housing." and I was like "this idiot hasn't figured out what he's gotten himself into." And i realized that he needed to go through it to see what the reality was.
I was spitting tacks on the inside, btw. I wanted to KILL that woman. But she wasn't in my social circle. I wasn't in the same social circle that my husband was in this instance. This was a circle that was wholly his -- and in this circle, these illicit relationships were common. DH would say "it's terrible! terrible!" and I know he feels that way. But he didn't see how he was walking right into a compromised situation.
Seriously, he's an idiot sometimes.
Anyway, he goes out to her place and the first night he's knackered and he immediately excuses himself and goes to sleep. He noticed the way that the other women who were there behaved when he arrived, and he was like "oh, this is like when a girl likes a boy and all of the girls go "oooooo!" but he said "oh,t hey're probably just being silly." The next morning, she started the seduction processes, and he was pretty oblivious because he was excited about his meetings.
She then arrived home in the evening just after he did with wine and movies, but my husband doesn't drink wine, so her advances didn't go very far, and he went to bed. The next morning, she completely flipped out on him. . . something about "not meeting her needs and expectations" and he was like "what?"
Seriously, he's an idiot.
So, anyway, he went to a hotel for the rest of his stay (about 4 nights). And when he came back, we debriefed about what really happened, and I showed him all of the evidence and signs from day 1 that I was aware of and how it fit together. And he was completely shocked because that's not how he saw it at all. And he felt bad (and stupid), and apologized to me for putting me through having to wonder if he was going to cheat just because he got himself into a pickle.
I am still no fan of "that woman." I've never met her, I've never had contact with her, but I wanted to cut her to ribbons when she openly invited DH to stay at her place for the time that he was there. I could tell in the email (and I told this to him) that she perceived this as the time they would take their relationship to that next level.
So, part of me was just having to trust my husband and my process while KNOWING that this woman whom I didn't know was trying to draw him away from my relationship, with no consideration toward me (or him for that matter) or our relationship. And it SERIOUSLY pissed me off.
While today (nearly 8 years out?), I have very little emotion about it per se (as nothing really happened thankfully), I would still cut her if I met her. And by that I mean verbally, and not physically. Because, honestly, I would hold her accountable for her actions against me and our relationship.
I've already held him accountable. But she's *never* been held accountable. And as such, I still hold out anger about it.
And for the record, my husband openly shared emails/etc with me -- I do not look at his. He literally thought that she was just beign "funny" and not interested in him.