If the problem is that Facebook provides an echo-chamber that exacerbates the influence of one particular viewpoint, wouldn't the solution be for Facebook to begin injecting opposing content directly into the newsfeed?

You can kind of see this with trending topics. If you don't follow a particular topic but suddenly see it trending in your feed, there's a chance you may random walk into clicking it. If Facebook opens up a global/regional/local newsfeed that isn't highly targeted, then you could potentially start seeing more original content.