I think it's closer to say that I think it
could impact on the rest of the population. It depends a lot on how much you trust the state to stay within its narrow remit of targeting specifically those extremists who not only challenge the way we run our society but also actively stir up hatred and encourage violence and terrorism. Inevitably, in order to find all such people, you have to start by assuming that everyone is a potential terrorist and examine what they say, do, think, who they talk to, and so on. Otherwise you would miss at least those you are looking for and have to reply on their showing themselves in public discourse. Some already do, of course. Others are not so visible, so would need to be found by, effectively, automatically assuming guilt until established otherwise.
Already that's one of the fundamental tenets of British society potentially thrown out of the window right there. If this is not what Cameron meant, it is certainly what he said when talking about interfering in people's lives "even if you are within the law".
And what guarantee do we have that it would stop there? Several years ago there were stories about councils using what was meant to be anti-terrorism legislation in order to deal with things it was not meant to be used for. Abusing the powers, in other words. And those were just local councils just getting obsessed about dog owners.
It is, then, a legitimate concern to be worried about what greater state interference will mean. Will these concerns turn out to have been justified? I don't know. But allowing the state carte blanche to interfere in other people's lives will inevitably lead to its interfering in and snooping on yours. That could well be a negative impact and it's dangerous to dismiss such concerns as idealistic or naive.
It's important to try and tackle extremism. It's just also important to make sure that in doing so we aren't abandoning the values we are protecting.
http://www.telegraph.co.uk/news/politics/7756352/Councils-using-anti-terror-laws-to-spy-on-dog-walkers.html