Twitter’s terms of service are clear:
You may not promote violence against or directly attack or threaten other people on the basis of race, ethnicity, national origin, sexual orientation, gender, gender identity, religious affiliation, age, disability, or disease. We also do not allow accounts whose primary purpose is inciting harm towards others on the basis of these categories.
As you can expect the banned account holders are none to happy and are responding in the fashion that got them banned in the first place. Said Richard Spencer,
“I am alive, physically, but digitally speaking, there has been execution squads across the alt right. It’s something like the Night of the Long Knives [Adolf Hitler’s 1934 killing of several Nazi leaders].”
“It is corporate Stalinism,” he continued. “There is a great purge going on. They are purging people on the basis of their views.”
Look, if you spew hate and advocate violence then you shouldn’t expect that you are going to be allowed to do it on a social network, especially when you signed the terms of agreement when you created your account. The First Amendment prevents the government from infringing on your right to free speech, it doesn’t prevent Twitter from banning you for violating their terms of service (that once again…and let me make this clear YOU AGREED TO WHEN YOU CREATED YOUR ACCOUNT).