Having a civil back and forth discussion about a topic is fine, it's when it turns into an all out war that it becomes a problem. That all being said, there will be times that we pre-emptively tell people to calm down so as to prevent things from spiralling into bullshit, though that doesn't always work. Its difficult to talk around two people who are hell bent on proving each other wrong and In most cases those two users would be dealt with alone and the discussion would continue, but if the thread has a tendency to spawn the same type of crap multiple times than its better to end it lest it turn into a constant problem.
Saying something like 'you're limiting discussion' is kind of a stretch considering the fact that we allow almost every kind of discussion outside of NSFW topics. We just want to make sure the discussions we DO allow remain civil, if that means we have to lock a particular thread because it turned into a lure for bullshit then so be it. Doesn't mean we banned the discussion.