The blame for Ben's death still ultimately lies with Fisk (and the woman at the newspaper who tipped him off). In case you've forgotten, Karen was very nearly murdered for her mistake as well.

It's like Claire nearly getting murdered because of her association with Matt. It wouldn't be fair to blame Matt for what happened to Claire, because Matt can't control what other people do. Just like we can't blame Matt for Elena's death, just because Fisk wanted to make a point.