The truth and the courage to speak it undermine tyrants.
Technology is an amoral, double-edged sword. It can be used to rapidly disemminate it, but it can also be used to crack down on, and distort it.
Yes, tech is a two-edged sword. But, the point is the particular technologies we are discussing here are, by design, difficult to control. Now that people have the tech, they will notice it being taken away and immediately react. Governments have lost the ability to control the message to the degree Hilter and Stalin had.
Plus, you can get the word out to a large audience before you are silenced (public life insurance) in a way you could not standing on a soap box literally on a corner in some town somewhere. Those people disappeared long before many people heard their message.
Even if the government acts on what you said, they cannot make it unheard even if it they delete it from the outlet.