It matters very much with regard to the distinction between yours and theirs. I strongly believe the operating system of your device should never actively work

It matters very much with regard to the distinction between yours and theirs. I strongly believe the operating system of your device should never actively work against your interests, and checking whether you're using the device to commit a crime, then reporting it to the device manufacturer who will tell the government is potentially strongly against your interests. If that's too abstract, it matters in that it's a foothold for further scanning of data on your device. Without this system, if a state wanted to pressure Apple to create spyware and add it to their operating system to look for something else, that would have been easy to refuse. With this system, the spyware is already there, and despite Apple's protests to the contrary, it's just a matter of a few tweaks to repurpose it.