North Korea is totalitarian. Nazi Germany was totalitarian. The Soviet Union was totalitarian. Criticising the government could get you executed, or imprisoned in a far away forced labour camp for a long time.
Quora is a website. They can, er, ban you from using their website. That might be a stupid, not very nice action for them to carry out, but it's not totalitarian.
First they ban accounts and sometimes delete them to make the person disappear without a trace, and secondly they prohibit you from asking why certain people got banned. This censorship prevents people from acknowledging that certain people existed.
Criticising Quora on Quora will get you banned without prior warning, and in some instances have your account deleted without a trace.
And when you're banned or disappeared, nobody is allowed ask why that happened, as those questions get censored.
Think of it like this when you criticise Quora. http://upload.wikimedia.org/wikipedia/commons/9/91/Voroshilo... http://upload.wikimedia.org/wikipedia/commons/b/bd/The_Commi... And then being censored when you ask why the person force disappeared.
see: http://en.wikipedia.org/wiki/Cubby,_Inc._v._CompuServe_Inc.
And the subsequent Section 230 of the CDA: http://en.wikipedia.org/wiki/Section_230_of_the_Communicatio...
In no way was it implied that an ISP or other information transfer network (ie. the post), had to moderate its data transfers.
This is about the specific service that uses the network, not the network.
But you are right, if company employees are saying things specifically about people that would be considered libelous that's a problem.