A little perspective goes a long way. I see the ignore feature as a temporary tool - like the "show/hide all characters" feature in a word processor.
In a long thread with a many side tracks you can clean it up for an easier read by removing the people having unrelated side conversations. This is no different to me than hiding all the tabs, spaces, and paragraph markers in a Word document.
If I want to ignore or avoid exchanges with a given person well, I don't need a feature for that.