Why would established members "have to worry too much about how any particular post received" if HN didn't have karma?

You say that karma allows established members to "present unpopular points of view without too much penalty" but how does karma's existence (that is, the total of all up-votes on all comments and features gated by that score) not encourage just the opposite? Also, why should we privilege established members' dissent more than outsiders'? It seems like outsiders might even have a better vantage point.