Nonfree (proprietary) software is very often malware (designed to mistreat the user). Nonfree software is controlled by its developers, which puts them in a position of power over the users, and that is the basic injustice. The developers and manufacturers often exercise that power to the detriment of the users they ought to serve.
This typically takes the form of malicious functionalities.

Code:
https://www.gnu.org/proprietary/malware-apple.html