Downvotes hide discussion, and upvotes make them more visible. That's not what you want if your goal is to eliminate the echo chamber. Perhaps we should change the default sort to sort by controversial (i.e. lots of votes on both ends).

For example, let's say there are two comments:

1. funny comment largely unrelated to the topic
2. detailed comment with extensive sources, but goes against the common opinion

The first comment is likely to be near the top, and the second will likely be buried near the bottom, and perhaps hidden (e.g. Reddit auto-hides if a comment goes too negative). That's not what you want if your goal is to have productive conversations.

From my experience, people are less likely to click the upvote when they agree with something or think it's relevant than they are to click the downvote button when they disagree. For some reason, disagreement is more likely to provoke a response than agreement. So if you eliminate the downvote as an option, you'll likely get people only voting on things that are relevant or really important to them. It doesn't solve the whole problem, but it at least seems to help a bit.