They aren't
indiscriminately doing anything. Only executables with hashes not previously seen are sent by default, and clearly you know how to turn that off.
They're legally bound by their privacy policy. They can't use info obtained by those executables to blackmail you or turn you in to authorities; they can only use that data to improve the anti-malware service they offer. And, as previously mentioned, you know how to turn it off.
The information about this isn't hidden. An operating system is complex, and thus operating system configuration is likely to be complex. Microsoft could have made things less difficult to find, you're right, and they are basing their defaults on the vast majority of people, like me, who are completely fine with doing what we can to improve their anti-malware service.
You're angry and that's fine.
Imagine the anger (and the fallout) if yet another malware worm used Windows to propagate across the world. People were absolutely LIVID last time, and there were lots of lawsuits against Microsoft for ILOVEYOU and Code Red and others of the era. The default settings you see today are a direct result of those events and other, smaller ones, like them.