While group-think is real, the views that are allowed to be expressed on Reddit were not selected because a majority of users held them and pushed out those who disagreed. They were selected by the corporate owners of the site to promote their ideological beliefs, and to appease the very similar ideological beliefs of the major corporations who buy ads there.
Contrary opinions were driven off the site simply by repeatedly deleting the subreddits and users who expressed them. Down-voting or any other organic user interaction had nothing to do with it.
Placing corporate representatives as moderators is just a way of preventing the organic accrual of power to those with popular opinions that challenge the ideologies of the site owners.