Quora's case is very clear cut. They derive all of their value from their users, the user created content. They then put protective barriers in place to prevent access to content others created.
For example Quora's robots.txt explicitly prohibits the wayback machine from crawling anything on quora.com. The &share=1 is a hack to trick googlebot, if Googlebot were capable of indexing registration required content, Quora would probably not provide this share=1.
Quora's technology is a glorified textbox and some links that link to content. The value is all the stuff that others have added to it. Which in itself is fine, it's something companies like Yelp do and do well to everyone's benefit. But Quora's policies again and again show a complete disregard for the public and even its users:
Requiring a real name.
No way to delete answers or questions easily (you can email to have your data deleted, which I did a long time ago).
Requiring a log in to read content (I wonder if you could convince some uninformed federal prosecutor that the share=1 trick to get around the block can be used to prosecute someone with the CFAA)
Blocking the way back machine and their shitty robots.txt
Not so long ago the hiring page on Quora asked candidates to be ready to dedicate their lives to the startup, to make it the primary focus of their lives which I thought was such a horrid thing to ask of an employee and really subtext for hiring discrimination based on age.
Quora managed to get a lot of funding because of the notability of its founders. Notability derived riding Mark Zuckerberg's wake. My opinion, based on their actions, is that these founders are evil arrogant people who think little of others including their employees, their users and the general public. Their mission is not any noble cause to share information, it's aggrandizing their self-importance. And I'm so happy that Quora is a floundering ridiculous mess of near no value. I just know they'll eventually purposefully transition into a shallow content Demand Media ehow clone. Because someday they're going to have to account for all that money they took in. They'll do that, and then a Google Panda update will kill their shit and that will be the end of it.