This was originally one of the features planned for 0.14.0, but after a massive backlash about censorship, the feature was dropped.
People were completely against what you're suggesting. View the discussion about it here: https://github.com/steemit/steem/issues/279
Thanks for bringing this to my attention.
willbanks made a great observation:
Really interesting discussion and I'm glad you pointed me there.
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Update: I didn't mean to upvote myself. It was a slip of the finger, but now it won't let me undo it.