As people can filter users or tags that they don't want to see, and as their feed only contains what they follow, much of it is done on the individual user level.
Some content is filtered from the global feed, and we rely on user filtering statistics to identify content that might qualify. You can see the unfiltered global feed if you like (there's a toggle in your settings) to see everything that is submitted.
It's worth noting that we cannot ensure thoughtful discussion happens, and that that's the only kind of discussion. Users can moderate discussions on their own posts, and it's up to them to decide what kinds of discussions they want to host.