This is exactly what good moderation can help with -- promote thoughtful and reasonable content, while making sure that inflammatory commentary gets less attention. I've run an online forum for over a decade; it's not that hard, really, to encourage thoughtful participation, with the right type of leadership.
See what dang wrote:
> please don't post low-information, high-indignation comments, such as flamebait or ideological battle. We want thoughtful, curious conversation on HN.
The problem is that big social media is so large and "open" that they don't want to have any community leadership.
Who is setting the tone on Twitter, or any major social network? Who is acting as a leader, both enforcing quality commentary, and also setting a good example? Nobody. I doubt this will change.
Smaller communities, such as HN, are where we can have reasonable discussion.
A good correllary: many local city council meetings, where almost anyone can have a chance to talk. They're not pretty. But at least the decision makers are there (and held accountable), and limits are set.
Creating an environment where good discourse can thrive is hard. It's like fighting entropy. You can do it. But it's an uphill battle.