Nothing can be removed from the Steem blockchain by anyone. The reality is that it is very difficult to prevent anyone from plagiarizing your content if you make it public. That is one of the reasons why with OpenSeed we are putting a lot of thought into how we enable creators to control who gains access to their content, and providing those creators with the ability to charge people for that access. Your public content should function more like an advertisement for your private content which only a privileged few have access to. This also makes it easier for users, communities, and creators to police plagiarism.