Calling the violent mob attack on the Capitol what it was: sedition... by federal statute definition and the penalty: 20 years. On this basis alone, social media taking down posting with plans, supporting and coordination of sedition like Twitter have a firm legal ground. In their use as the communication vehicle for those committing sedition, sites like Parler that plan to continue as the platform for sedition need to be considered as those aiding and abetting sedition. This is not a freedom of press or first amendment rights issue. There is nothing in the Constitution that protects those who incite revolution or violence against the US. Parler's Amazon server platform was taken down late January 10..
Update 1/10/21 https://www.cnn.com/2021/01/09/tech/parler-suspended-apple-app-store/index.html