All states,
including Iran, have departments concerned with monitoring, detecting and also exploring the possibilities of exploiting what could be called vulnerabilites in modern systems.
And you're absolutely correct in that monitoring capabilities have always existed well before the Web, but where you are wrong, is that the CIA/NSA/GCHQ etc are interested in you.
They're highly likely not.
It's about keeping the barbarians at the gates, they do exist, from without or from within, and monitoring those who wish us harm and to damage or destroy the very fabric of our societies, with the actors ranging from kids in the Phillipines who want to crash and trash International Banking systems for the LOLs through those seeking commercial or military information or simply financial blackmail or large scale People and Drug Trafficking and then beyond to sophisticated government funded teams with malicious intent seeking ways to close down power grids for example.
Of course State knowledge of many of these very same techniques also provides any State with a possible new means of waging warfare, for example instead of bombing a power station or a telephone exchange, if you can simply disable it while sitting at a desk 5000Km away it's undoubtedly an attractive and much cleaner proposition should all out conflict erupt and it's certainly got to be better for those working in such places than having a high brisance event unexpectedly delivered in their faces from someone up on high.
But the bad people are not going to go away, anarchists and bastards with evil intent will always exist, and if the CIA/NSA/GCHQ etc were dissolved, I can assure you that within 24 hours new departments would have to be created and will be carrying on doing exactly the same thing.
It's all part of what is referred to here in the UK as
Defence of the Realm, and it's something we have always and will continue to take very seriously, and it would be remiss of us not to.
And unlike those who live in Iran, we here are pretty much free to browse wherever and whatever we want.