So, if a user is ignoring another user, it prevents the 'ignored' user from participating in a thread that the 'ignorer' is a part of.
This defeats the purpose of having a useful community. If someone being ignored prevents them from participating in threads, I'd have to cast my vote in the box that says "fix this ****, because it's stupid".
I'd suggest that if someone is being ignored, then the ignorer should see said persons post as "hidden". This seems completely fair and reasonable because everyone that is a member here has the right to participate.