This is the wrong threat model, I say more here[0]. There's a difference in threat model when you're an individual vs part of a large protest/revolution. A government can't arrest everyone. They can definitely get a mole into the encrypted discussion (even if it isn't technological). You can't vet hundreds of people in such a short time. Protests and revolutions have been organized in the open on Facebook and Twitter for exactly this reason. Because it doesn't matter. You're going to go out and show your face to CCTV anyways.
[0] https://news.ycombinator.com/item?id=33400739