The “harm” is the literal murder of black people, transgender people, gay people, etc. The tweets don’t do the murder, but status quo the tweets are supporting does.
I think some here, when talking about freedom of political speech, lose sight of the actual stakes behind the politics.
I'm definitely against any tweets calling for the murder of anybody, I'll say that. But the "anti-harm" movement is not as benign as you think. For instance, see the firing of David Shor, who merely tweeted a study comparing the effectiveness of violent and nonviolent protests. There's an instance of someone who tweeted AGAINST harm, in that he was advocating for nonviolence. Yet he was still censored.
I think some here, when talking about freedom of political speech, lose sight of the actual stakes behind the politics.