As I said, it's not impossible, nor is it difficult for technical reasons, it's just more difficult because there's more stuff to block, and you'll never find every little server setup by a few activists to access the network. With proper encryption (or even basic TLS to the server) it also becomes difficult to do deep packet inspection (which is hard to do in the first place). The example I gave before also still stands: Look at the last time Egypt tried this. They attempted to block email and SMS temporarily and various activist groups just setup their own servers to get around it. Not every random user can do this of course, but it's important that at least some activists can.