To me, privacy is about control (deciding who gets to see what) and having an OS that phones home with who knows what information means I have no control once information touches my PC.
And that's an understating.
An OS can know all your passwords, can look everywhere around on your network, can sign documents legally impersonating you.
Which is often enough to completely divorce you from your identity legally, steal all your money, and possibly incriminate you.
That's all. But hey! My porn browsing habits are SAFE ON MY OS.
Of course, there's always the chance that Microsoft is lying in their documentation, but if you mistrust them that much, you probably shouldn't use their software even if they claim to not collect any information.
Last I looked Microsoft's privacy policy was vague enough that it could include almost anything and everything on a PC as well as whatever Windows can infer about your local network.
> Of course, there's always the chance that Microsoft is lying in their documentation, but if you mistrust them that much, you probably shouldn't use their software even if they claim to not collect any information.
You're right, at the end of the day it comes down to trust. Microsoft's behaviour in this case - making it hard to disable telemetry, being vague about collection details and unresponsive to questions - means that it's hard to trust them. In a hypothetical world where they were upfront with what was collected, responsive to questions, and allowed users to disable all data gathering easily the same feature set might be easier to swallow.
Edit: I forgot to mention how aggressively Microsoft has been shoving Windows 10 down user's throat. I've had several non-technical friends end up with Windows 10 by mistake (and against their wishes) - another sign that Microsoft doesn't give a shit about users' wishes.