It doesn't mean anything whenever people can identify trolls or not - a discussion can be harmed even if troll activities are obvious. On open platforms, where

It doesn't mean anything whenever people can identify trolls or not - a discussion can be harmed even if troll activities are obvious. On open platforms, where participation is not limited, they can hinder the discussion by intentional, completely retarded name-calling, swearing, utter off-topic and alike - and moderation isn't really effective as individual accounts are essentially a cannon fodder.