it is quite reasonable to be worried
About what, exactly?
Could Microsoft copy all your files to a remote server? Sure, at least in theory. But what exactly do they have to gain by doing so?
Are you involved in treason or sedition via email? Is your hard drive full of pirated software or kiddy porn?
If not, then this is all merely a philosophical debate, and while I agree that corporations and governments shouldn't spy on their customers/citizens... It's not like I'm going to lose sleep over the fact that they do.
Until the point comes where you need to engage in sedition. Or when you need to maintain commercial secrets from your US competitors.
The right to privacy should be held higher than the right to bear arms when it comes to insurance against tyranny. Tea Party idiots should be foaming.
As mentioned earlier, it's not just the terrorisms and sepratists and paedobears. If you're working for a non-US high tech company (telecommunications, aerospace, defence, crypto, energy, etc) then you're a target. Or if you're an activist of any kind, or a journalist, or a "lefty intellectual" with an audience, work on key open-source libraries, involved in petty crimes, facilitate IP infringement (even via legal loopholes), or if you publically sympathise with Palestinians, Syrians, Iranians, Russians, etc...
There's people out there trying to publicise the fact that the empire overthrows democracies, installs nazis, funds islamists, knowingly breaks the laws of war, kills journalists and doctors, tortures, kidnaps, basically does whatever it takes to ensure that the empire grows in strength and that it's competitors are contained. And these people are treated as traitors - they are spied on, framed, hunted, destroyed, even to the point where it's acceptable for politicians and pundits to publicly state their desire for assassinations of such truth-seeking "traitors". And MS is now working as a tool of that empire.
When it comes time for sedition, keep a 90's era Linux dual boot and a sneakernet handy :lol: