Speech is never really free. It always comes with costs, consequences. (When I was first ordained I decided to stop using certain words, knowing that I would not always be aware of who could hear me. That minor display of wisdom may have saved me from serious trouble.) The consequences of allowing Parler to be used in planning and carrying out an insurrection might reasonably include having to find a new host. The consequences of spreading lies about an election might well include losing customers.
I don’t want to stop you from speaking but I don’t have to do business with you.