I have a lot of great conversations on Facebook, typically better than the conversations my blog posts elsewhere. It's a matter of cultivating a good community.
In my experience, reddit and other online discussion forums have been just as bad as Facebook at times.
Online communities like reddit and, yes, HN, are echo chambers to varying degrees. They can also elicit a sort of inhumane treatment of others by depersonalizing them, sort of like what happens when people get behind the wheel of a vehicle.
Sometimes I have commented on facebook forgetting it was not HN or another niche community. If you start talking about how your country's weather bureau monitors itself for forecast accuracy then you will almost certainly be met with silence if you try to do that on facebook.
That's the one thing I absolutely loathe about Facebook. There's no constructive dialogue going on. Everyone is so full of themselves that any kind of argument derails pretty fast. And then there is the fact that the platform doesn't provide the structure for long conversations. After a couple of replies all text has the same indentation so it's hard to see who's responding to what comment. I've been online for twenty years, and I've never seen a environment more hostile to conversation than Facebook.