There are many specific things that would take awhile to talk about. The worst thing is the fact that spies can go in and search and seize, unreasonable search and seizure, and break the Constitution that way. They can take anything and remove anything.
Basically, if we had 100% trust in our security services, everything would be fine. We know mistakes get made. We know that power gets abused, and if this power falls into the wrong hands, anything goes. People could get framed for something they didn't do. People could have something installed on their computer that they never put there. The limits are endless.