This is not about trying to control the terrorist groups. They will organize however they can whether that be through the mail, newspaper classifieds, telephone or even secret hand shakes and other cryptic activities. Those have all been used over the years prior to the Internet - I don't see anyone calling to regulate any of those options. Why?
Because it is more about controlling the narrative than it is controlling the terrorists. It is, and always will be, about controlling the larger masses.
I am in Arkansas. The middle of the United States. Thanks to the Internet, within four fours of the attack I was able to find out via social media and websites (even some articles here on Steemit) that there was a bad situation over there. I even did my best to pool together a few of the news stories into one in hopes of helping anyone that read my article to have a better understanding of the situation.
Now, if the government controlled the Internet like the British Prime Minister wants, I would have probably not heard about this sickening event for a week or two. Just like it was in the 1960's (at least how it was as I was told since I was born in 1976). Government wants control and regulation so they can tax and destroy anything they deem unworthy of existence. The Internet is nothing different to them. They want to use terrorist attacks so they can pass legislation to inhibit activities of the citizens.
Just look at 9/11 here in the United States and how quickly, the useless, TSA was implemented and people all of a sudden were fine being literally strip searched, in many cases, in exchange for the privilege of flying. I don't know of any other country that does this to their citizens prior to boarding a plane and those countries send as many, if not more, planes into the sky to land somewhere else.
Regulation is control and the ability to eventually destroy. Remember that.