Everyone is applauding this because they hate Trump, but take a step back and see the bigger picture. This could backfire in serious ways, and it plays to Trump's base's narrative that the mainstream media and tech giants are colluding to silence conservatives (and maybe there could even be some truth to that.) I know the Valley is an echo chamber, so obviously no one is going to ever realize this.
There is no such requirement.
Twitter is well within its rights and ethically totally clear to "police" a sentiment from the President of the United States, while letting much more severe sentiments from egg accounts go un-policed.
Moderation isn't an algorithm, a binary condition, applied perfectly to an input set to get a deterministic output. It's subjective, and that's both OK and correct.