SBC's argument is self-contradictory. On the one hand, he paints tech companies as greedy, untrustworthy, and arguably evil. At the same time, he feels that these companies should be trusted to regulate speech to a degree beyond what they already are doing. (In his example, through regulatory force telling them to do so.)
In general, he wants the end (no "bad" speech) but doesn't provide a clear picture of the means to get there. This is common.
The argument against companies regulating more speech is that people who are not Nazis will be caught in the crossfire, and that will lead to unintended consequences. In his speech, SBC admits as much, citing Twitter's claim that algorithmic regulation of speech would result in de-platforming politicians. SBC claims that this may not be a bad thing. This illustrates the problem: SBC like many others are perfectly fine with people being de-platformed not just for true hate speech, but for speech they disagree with, because it is algorithmically similar to hate speech. This is the crux of the issue, and it's at least good for someone to admit it: typically proponents of centralized speech regulation pretend like the issue of false positives doesn't exist. Such false positives will result in law-abiding citizens being de-platformed, and that is unacceptable to many.
To whatever degree that strategy is taken, you can bet your money on these companies losing their power to decentralized platforms. If it's no longer possible to post on social media without a reasonable risk that your words will get nuked because of being mis-flagged (and your reputation unjustly soiled) -- people will move elsewhere. The irony will be that the net effect will be way worse than today: completely unmoderated, unregulated speech with global reach. (this is probably inevitable for a variety of reasons, but this current dynamic probably accelerates it.)
edit: appreciate the downvotes, feel free to check back here in 10 years when facebook + twitter are no longer serious platforms because they're policed by over-zealous, government-mandated moderators, and anyone posting anything interesting is on a decentralized platform or some new centralized platform which has yet to be put under public scrutiny.