When you use a proprietary OS, you rely entirely on its creators to create a system that does what you want. When something in Windows or OS X is not what you want (or is broken), you can't do anything about it. When something in a free OS is not what you want, you always have the option to use something else.
Free is about transparency. Not snooping on my files, do machine learning mumbo jumbo on my habits, surreptitiously nudge in the direction they want is huge part of it.
Free is a promise, a promise that I do what I say. If the software doesn't, it is for all the world to see my deficiencies.
Free is also about not being an asshole. It is about accepting the fact that, just because the users use my software, I don't get to control their lives.
When you use a proprietary OS, you rely entirely on its creators to create a system that does what you want. When something in Windows or OS X is not what you want (or is broken), you can't do anything about it. When something in a free OS is not what you want, you always have the option to use something else.