By that logic you would hold the phone company responsible for calls and texts happening over their network.
Meanwhile google etc are pretending they are neutral carriers while actively filtering and choosing what is shown, now politically, showing they not only have the capability to control their platform but put it in practice.
If they cannot allow others free speech they should not get special protection that prevents their liability.
If a phone company started filtering political discussion I would absolutely think them responsible now for everything on their network. Your example is perfect to show how different both groups are in capability and practice.