I don't think we should ignore platforms that call for violence, but is that what Parler did? AFAIK, only people using Parler was inciting any violence, not the people actually running and maintaining the service Parler.
Go ahead and complain to their service provider and see if they are violating their ToS.
The big difference is that Twitter and Facebook actually (poorly) police their content where Parlor refused to do anything to block calls to violence. They were warned and continued to violate the ToS and AWS decided to walk away from the relationship.
What good if having a contract if you aren't allowed to terminate it once a party violates it?