Picture on flickr tagged with porn

Hey, I am really wondering myself why there isn’t sex, porn or other explicit stuff on flickr. There are in fact some blogs, who select “best of the soft porn on flickr” like softr. But there is nothing explicit on flickr itself. How can this be? Does this stand in the terms of the agreement when signing up flickr and people do agree in fear of loosing their free acount? Do the people at flickr have censorship? Or do they have a technical solution for this? Or maybe all flickrusers are so very intellectual and only apply to sensual and soft?
Also the comments under the more “arousal” pictures always give respect to the people who loaded the pictures up. There is “Hey, cute picture” instead of “I wanna f*** with you”. There are no trolls and no flamewars. How can this be? Are we experiencing the BETA version of the utopian internet here?