The reason I dislike this, is that besides obviously racist or otherwise inappropriate comments, there are regularly normal seeming comments that are dead. Now, there may be reasons for this I am just not privy to, but I feel it hinders discussion when some opinions that don't seem problematic are just silenced like this.
[Edit]: And rereading my own comment, I think I want to clarify that I am not talking about free speech issues or political discussions here, but I regularly encounter factual seeming or explanatory comments in technical discussions that are dead and it just baffles me.