I could knock up a P2P messaging solution that used end to end encryption in an afternoon. I could then share this with my evil friends and they would know very little. This is nothing more than scare mongering so that the government look like they are doing something to protect us when they don't have the first clue.
We used to have "effective" (couldn't think of another word) terrorists in the UK that didn't use the internet, end to end anything, mobile phones, etc. They managed to indoctrinate and share information and training quite well enough. We couldn't really stop Irish terrorism then and these knee jerk plans by an ineffective bunch of clowns won't stop Islamic terrorism now.