I don't know about social good, but we once tried to get the HN community to help pick startups for YC to fund. This failed, not just in its top-level outcomes but also in most of its details along the way. A community like this doesn't respond well to "harnessing". Trying to bring it into any purpose-driven order seems to have a dumbing-down effect. Genuine intelligence, to the extent that it shows up, does so in the small, randomly, and without a purpose. If you try to make it happen in any predictable way, that discourages it. There are a lot of counterintuitive effects like that.
Edit: but I should say something positive too. If you do find a way to join forces with others in a project for social good, or anything else really, you can often get surprisingly interesting feedback from the HN community about it. It will just be sporadic.
One of these years I want to work on ways to support HN users to form more real-world connections with each other. It seems like that could lead to projects and collaborations that otherwise might never get started. Whether these were startups, efforts for social good, or whimsical side projects, it seems like people's lives could be enriched, and maybe there would be good effects beyond that.
