The idea is that it would be impossible for Twitter to remove every single Tweet that's libelous, threatening, etc., and so the only way to avoid being sued is to not remove _anything_. That ends up being a policy that is favorable to people who want to spread disinformation.
It would probably results in a mass exodus of discussion on the internet as every single platform from Twitter to niche forums on obscure topics suddenly were not allowed to perform any sort of moderation without incurring legal liability. Thus the decision to abandon the discussion venue or watch it descent into something resembling the toxic cesspools seen in places like 8chan.
