1. It is not censorship. The government is not shutting down free speech.
2. Calls to violence, are not covered under the 1st Amendment, even if they government was calling the shots.
Non-governmental business are free to boot customers for violation of their terms of service. It's not a right for anyone in America to do things that violate private sector rules. You are not entitled to use the RF site you are on, for example, to call people to arms against the U.S. Government. You will be banned. Nothing to do with free speech here. This is a private site.
End of argument.
I am amazed when people that supposedly advocate for the free market get angry when businesses tell people and organizations that they cannot use their sites to advocate violent revolution.
If one wants free speech in a capitalist democracy they have several options. Go to a public square anywhere and state your beliefs loudly. As long as you are not trying to disturb others this will be allowed. Go up to people and shout in their face and even this activity will be curtailed. Find a business that is willing to help spread your message. Don't worry, there are plenty out there for any message. But if a business looks at people and say "These people are past being Fruit Loops, they can't post here any longer" as a supporter of capitalism one really has not valid complaint when that happens.
Twitter sees people lying as harmful to America.? They can shut down those people and remove their posts. Those posts are a long term threat to their business model. As a capitalist that should be supported. Business that Parler uses to get their messages of violence and revolution out and want no part of it. That too is their right and a capitalist should support it.
If your views are so loony as to be only supported by sites that almost no one visits then it might be time to look at one's beliefs again.