Reddit's current structure very much produces an echo chamber with only one main prevailing view. If everyone used an extension like this I would expect it to increase overall diversity of opinion on the site, as things that conflict with the main echo chamber view could still thrive in their own communities rather than getting downvoted with the actual spam.

Hacker News structure is identical though. Topics invite different demographics and downvotes suppress unpopular opinions. The front page shows most up voted stories. It's the same system.