Is it right if UK intelligence services can tap into our private messages?

I am from the side of the debate on surveillance that supports intelligence interrupting our private messages on phones and the internet. I see the security and safety of citizens to be of utmost importance in the UK and globally. I also believe if you have nothing to hide, why does it matter that people might be able to access your private messages? These people do not know who you are, and therefore as long as you're not causing a danger to anybody else, your private information would go nowhere. Intelligence services like GCHQ in the UK are there to keep us all safe. It is because of the work they do that many terrorist plots are foiled before they manage to carry out violent acts. I therefore am all in support of the work they do, and how they do it. If you have nothing to hide, why should it matter?