If I hired a messenger to take a spoken message to my partner across town, the same applies. Nobody has any right to interrogate my messenger and he has no obligation to answer.
If I send electronic messages it should be no different.
The fact that interception and surveillance is possible doesn't suddenly make it obligatory.
Technology is power, in whatever form it comes in from weapons to education to communication. That power makes law enforcement more powerful and criminals more powerful.
Law enforcement wants it both ways. They want the increased power of their own encrypted communications, their own education, their own better tools and techniques AND they want to use technology to take away power that their supposed adversaries wouldn't have even been able to lose before the tech existed.
The technology exists. It can't be taken off the playing field. It doesn't matter how bad the "bad guys" are, law enforcement does not deserve that much power in a free society. The power balance between the state's monopoly on force and the people needs to be maintained. If it is not, abuses are inevitable.