So yes, according to the supreme Court, those posts are probably legal.
It would only be things like "everyone, let meet up at this specific person's house tonight and attack them" that would be illegal.
And of course someone could always take MS to court if they feel their First Amendment rights have been violated. The ACLU has supported the freedom of speech of the KKK and Neo-Nazis plenty of times, so it's not as if there aren't resources.
Also, while IANAL, Wikipedia says, with regards to the "Brandenburg Test" used to determine "imminent lawless action", there is a "bad tendency" test which may also apply:
"In Schenck v. United States[5] the Court had adopted a "clear and present danger" test that Whitney v. California subsequently expanded to a "bad tendency" test: if speech has a "tendency" to cause sedition or lawlessness, it may constitutionally be prohibited. Dennis v. United States, a case dealing with prosecution of alleged Communists under the Smith Act for advocating the overthrow of the government, used the clear and present danger test while still upholding the defendants' convictions for acts that could not possibly have led to a speedy overthrow of the government."
https://en.wikipedia.org/wiki/Brandenburg_v._Ohio
It would be great if a lawyer could weight in.
The article clearly states that the removed comments incite violence:
> "Microsoft received a complaint about specific posts on Gab.ai that advocate ‘ritual death by torture’ and the ‘complete eradication’ of all Jews. After an initial review, we have concluded that this content incites violence, is not protected by the First Amendment, and violates Microsoft Azure’s acceptable use policy," Microsoft said in a statement to The Hill.
Are you suggesting that this type of language should be protected by free speech laws?