I'm allowed to build a wacky unsafe DIY car and drive it around my own property without getting permission from the government. In many scenarios I don't even need a driver's license.

Bringing the analogy back around, maybe one could argue that if I let my phone get hacked such that it becomes part of a botnet or something then it is a danger to other people, but that's not the typical example. Usually these policies claim to be about protecting me from myself while using a device I own.