They are responsible for taking videos against rules down, still..they aren't responsible for videos being uploaded seeing as the rules state what you are or aren't supposed to upload. For example, someone posted a porn video against rules and youtube decided to finally take it down but someone is sueing them because "porn" was on youtube. The one rule "We aren't responsible for what users may put on there" basically just rips through that whole argument and the rule "No porn" gets rid of the video anyways.
If it states they have no responsibility for what is put up then they don't. But they still have rules to make youtube a safe place besides "porn" or basically something very bad.
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