This is true, it's definitely not perfect, but it helps. I think if people used the ignore feature, they'd be less likely to see certain posts, and would be less likely to make angry posts in response, and people would be less likely to see those angry posts and respond etc etc. But it's just as much about posters making passive aggressive cheap shots as it is about the ignore feature.
I think if you take into account a dozen or so posters adding another dozen or so posters on ignore, things would look a lot different. It obviously won't solve anything (as no forum I've seen has a "complete ignore" system) but I think it's a good start.