Who in their right mind would proudly proclaim their support for an organization that carries out bomb attacks on busy commuter streets during rush hour?
Quite a lot, as it happens: The ANC did that.
Who in their right mind would proudly proclaim their support for an organisation that tried to blow up the UK cabinet?
Well, quite a lot of people proclaimed support for the IRA.
Who in their right mind would proudly proclaim their support for an organisation that attacks a village and kills over a 100 civilians?
Quite a lot, given that a lot of people from Irgun (Deir Yassin massacre) have been central to the leadership of Israel.
The thing is, a lot of atrocities will seem necessary, or at least excusable, to those who see themselves as freedomfighters, whether or not the future will be kind to them.
I don't expect the future will be kind to IS, and the past is littered with terrorist groups - and freedomfighters - who are still hated and detested, and many of the ones "we" tend to see as freedom fighters today still have dirty hands and/or are seen as terrorists by others, so who knows...
I agree with the second part of your comment, though. It's played up because it's convenient to have enemies. Doesn't mean I don't think e.g. IS needs to be countered, but I don't think it'll get countered by snooping - on the contrary, it will fuel the paranoia of those that are intrigued by their cause.
To take a personal example: In my youth I was member of a marxist group. The knowledge that Norwegian intelligence services carried out extensive surveillance of the members of lots of left wing organizations (highly illegally, as it happens - but while the extent of their illegal surveillance was first "discovered" years later, everyone in the organisations in question knew about it; just that nobody believed them) did not deter me. On the contrary: It made me more certain my decision was correct: It was evidence of the oppression I was against.
The organisation in question was (and is) fully legal, participating in elections, and does not (and did not) advocate violence in any way, but I don't believe the overall principle is different: If someone is considering a cause opposed by government, then surveillance will not stop most of them, but spur them on and prove to them that they can not trust their own government.