The founding of America was based on insurrection. This western liberal value of speech you speak of is in your imagination because there's no where in the US constitution that says free speech is defined as anything except violence. Any decisions we made on interpreting free speech since its inception are purely arbitrary.
It may be true that those companies don't want to platform sedition, but what if rightful sedition cannot be achieved without being provided a platform? In that case, is it then up to companies to pick and choose which sedition movements they support by virtue of allowing them on their platform?
Yes. If you believe in a libertarian "absolute free speech" principle you should also let private companies decide who they let on their platform. You cannot have it both ways.
It may be true that those companies don't want to platform sedition, but what if rightful sedition cannot be achieved without being provided a platform? In that case, is it then up to companies to pick and choose which sedition movements they support by virtue of allowing them on their platform?