I think the point is well made about Youtube. There was indeed a huge amount of 'pirated' content on Youtube in the early days. Pinterest may be even worse because (a) the UI is specifically designed to make it incredibly easy to copy content. The overwhelming majority of Pinterest's content appears to be copied in this way. With Youtube at least people could and did upload a huge amount of their own content. And this is directly relevant to (b) Whereas Youtube was about hosting video content which may or may not have been copied Pinterest is so dominantly about copying content that it is much more like the case of the P2P sites whose whole modus operandi was to enable copying. It wasn't an unexpected or relatively minor aspect of their business - it was their business. And IMHO copying is Pinterest's business. The courts took a dim view of the P2P sites claiming that they were just the innocent service providers because of the overwhelming dominance of the use of the service and the fact that the site was designed to facilitate it. My suspicion is that Pinterest's moves to provide facilities to block pinning are legally motivated to fend off suits to the effect that they are unashamedly a copying engine.