To mitigate this, the non-shitty network should require a verified phone number. This is far from a complete solution, but most people have one and only one phone number.
Eventually, authorities could be established who vet the real identity of a user, and provide an additional badge of authenticity. (aka Twitters "blue chekmark")
It is generally a good idea to keep a rating for every user, so that content produced by assholes can be hidden.
The "downvote" concept employed by Reddit has a problem. It is used by people to say "I disagree" and ALSO "this is an inappropriate response".
The non-shitty social network would have explicit buttons for "I agree" and "I disagree". Disagreeing does not impact the karma of the OP.
Karma should be a ratio that you maintain, not a counter that goes up. Every user should start round ~50%, to give benefit of the doubt. If a user with good karma starts to post innapropriate content, their karma should tank.
A user's "karma" should not be impacted by the controversiality of their comments, but rather by their quality. A user who posts well-researched content with a controversial message should recieve good karma.
The main discussion of a topic often becomes overwhelmed by meta-feedback about the original post.
To enable meta feedback, each post could have a button to provide meta feedback, and nominate a postive or negative impact on karma. People will then vote up/down on the meta feedback.
A post may recieve positive feedback that the content was "well researched". People would upvote the "well researched" feedback, and the OP's karma would improve.
Another post may receive negative feedback that the post was "racist". Or it could say "this is false: ". People may upvote the "racist" or "this is false" feedback, which would negatively impact the OP's karma. This fix addresses problem #2.
Most posts turn into echo-chambers on one side or the other. High-karma-quality posts which recieve a lot of agree/disagree controversey should be bumped to the top of every thread.
Every page of the site should appear the same for all users. AI-curated news feeds will tend to exaggerate the echo-chamber problem.