Are Instagram, Pinterest and Tumblr Leading the Way in a Content Censorship Wave

Are Instagram, Pinterest and Tumblr Leading the Way in a Content Censorship Wave?

Do image oriented and visual curation sites have unique responsibilities since photos can be used as very specific maps for how to achieve certain negative activities, such as self-mutilation? Does the discussion expand to other social sites such as Twitter and Facebook, where I can link to such a picture? What about the role of general content arbiter aka search engines? Should our ability to look for and connect with potentially objectionable content at all be controlled?