It's not a non sequitur. Freedom of speech is not the same thing as a (nonexistent) right to post whatever you want on a private platform regardless of the consequences for others or for the platform itself.

I never said it's not censorship. You can post links on a number of competing services (or start your own), therefore statements like

“A group of unknown people at a technology corporation should be the ultimate authority on what I’m allowed to say, read, or share with my friends.”

are the real non sequiturs.