It gets so many visitors daily that when a site gets mentioned on its front page, the amount of traffic that then hits the named site will usually bring the web server down. And Slashdot too is entirely the creation of thousands of readers who discuss a wide range of technical issues most of which would be unintelligible to normal folk. They post new articles, read the articles posted, comment on them, and rate them. But they do not determine which articles appear on the front page of the site. That is now done a staff of reporters that sift through submissions and write their own content.
Editorial control is still in the hands of the people that set it up.
Unions would obviously also want to exert control over the content of their sites, even content created by their own members, in a similar way. Slashdot and the Open Directory Project are both enormously successful examples of teamwork. And this is something that the trade union movement has always been rather good at too. Which brings me back to that dying species, the webmaster. The one place in cyberspace where you still find the classical webmaster is on trade union websites.