Attribution is Still Important, Even on Social Media
Tumblr also doesn’t want users to create accounts with “confusing” URLs, i.e. URLs that could easily be confused for the official account of a corporation, a Tumblr user or a celebrity. Parodies are ok, no free speech will be undermined, but impersonation will not be tolerated. It’s a holistic approach to ensuring truth in blogging.
See here the initial post as well as related posts about the issue of copyright and attribution.