In the scenario of forcing speakers underground, those speakers have not been silenced (they may still speak to a large audience) but they will not speak to an audience which has not elected to listen to them.

Conversely, if you're popular on Youtube, you will be suggested to people who are not looking for your speech.

The difference is subtle, and that was my original point. Such acts of government will indeed not silence speakers, but it may as well do, because it stifles their ability to reach a greater audience.