Facebook comments
My issue with Facebook comments is the requirement to get a Facebook account.
I should not have to sell my soul to Facebook and abide by their horrific privacy policy just to participate in a public discussion.
Anonymous posting allows those with justifiable fears of retaliation to join the conversation.
The best commenting systems that I have seen let a user login using a third party email account, and have both filtering software that flags potentially offensive posts for review by a human moderator as well as a link in the message allowing users to flag a post as offense with a field requiring the user to explain why the user considers the post to be offensive.
I USED to participate in the discussion at my hometown Gannett newspaper, but Gannett's decision to use Facebook comments has excluded me.