If there were abusing it large scale, I still think it would come out ( cf Snowdon ) - the more people are involved, the more likely something is to leak.
ie in terms of conspiracy theories - those that involve large numbers of people being in the know, but nothing leaking, are the most unlikely.
However I totally agree that the recent trend towards secret courts, the attempts to remove access to a jury of your peers, and the creeping abuse of terrorism legalisation is both wrong and worrying.
However that's kind of my point - the existence of state powers of search isn't the issue, the issue is whether they are under proper control. The issue isn't whether the government can see the stuff I have with Apple, it's what's the process to allow that to happen.