They still don't quite get it..
There is no problem with surveillance for the purposes as described - provided that is indeed the use for it.
The issue is one of transparency and accountability, and the government scored a significant own goal when it retrospectively changed the law to legalise what GCHQ had been doing. As long as there is no transparency of the use of such powers, and no consequences for those abusing them there will never be trust, and the debate will never end.
There isn't a problem with giving law enforcement and those tasked with protection of any nation access to the tools they need to do the job. The problem is that with such powers comes responsibility and accountability - if you're unwilling to accept that, you cannot have those powers.
It's really no more complicated than that.