I agree, but I see the upvote button as a weak form of that. Good comments & those within the echo chamber rise to the top, but comments "outside" the echo chamber still stand a chance to be seen and considered on their merits. Also, the authors are not as discouraged to comment in the future which keeps a better diversity of opinion.

Perhaps upvotes and responses should be weighed similarly. That way garbage/spam can be ignored and fall to the bottom while discussion is still promoted.