Considering from a point of view stipulating that perfectly secure software is possible. I don't think it follows that the limititation that it would place on intelligence is necessarily a net loss.

Apart from the obvious harms of invasion of privacy, and fishing expeditions being biased to the places you decided to fish. There is the simple fact that data can be misleading, especially without context. An interceped communication is a piece of data that is intrinsically tied to the trust of the inteceptor. A few people with an agenda can collaborate to create a seeming truth by 'discovering' the same thing from different sources.

Requiring warrants compelling information holders to provide data, not only serves the task of protection from abuse but also create a record of provenance that can be verified.

It also provides a degree of symmetry in capabilities which discourages actions that one party may do over another if they are motivated to act because they have a temporary advantage over another.