The nature of systematic conversation ensures there will always be groupthink. Systems are designed to function in certain ways and deny other approaches to get their desired result. The result is that people who want this system flock to it, and people who want to somehow act counter to this system are going to be a minority that's possibly chased away by the system itself. Options like downvoting and "ranking" comments" and flagging inappropriate topics basically say that there is a right way to behave or talk, there are topics that are better than others. Then either people are attracted to the sites that reinforce their worldview or they're conditioned by these rules to decide there're right and wrong ways to think or to be – I'm not sure which it is. Probably a little of both.