Downvote is better than moderation imo. Its kind of leveraging the wisdom of the crowd. Free speech depend on this to survive. This has been a central argument in favour of free speech since inception.
In an ideal world this would be the case. But I think reddit has shown that people will most often upvote and downvote things based on whether they agree with what was said or not. That creates a scenario where the most popular opinion in the subreddit floats to the top and the fringe and challenging ones sink to the bottom. I think it's better to let the activity of a discussion dictate the position of posts rather than brownie points.