There are lists of Reddit and YouTube alternatives that are worth visiting. But they’ll only have a chance if we all try them out, evangelize them to friends, and post content (rather than just consuming it). The big issues are lack of content or early swarming from one political group (which then deters the “other side” from joining). Parler, a Twitter alternative, has this issue. I’m nevertheless trying it out just to give it a shot. But we might need a tool to manage the process of achieving quorum on what platform interested people move to. If we fragment across all of available choices, they’ll all wither and die.
Here are some starter sources of Reddit and YouTube alternatives: https://www.reddit.com/r/RedditAlternatives/comments/hi97fz/.... Also see https://www.reddit.com/r/YoutubeAlternatives/, which is newer and less developed.
Kialo is an interesting platform for debate - https://www.kialo.com/. But it is a complex interface and certainly doesn’t have the reach and accessibility of the biggest (and worst) platforms like Twitter. Apart from Kialo I think developing one’s own nuanced perspective is easiest to achieve by reading many different news sources and having respectful real life conversations. But only a few in my social circle are up for such discussions - I suppose it is better than none.
PS I feel your pain on the loss of Slate Star Codex. I had many bookmarked articles that I now can’t read :(