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I don't like Microsoft having that ability, because they screwed up the design of the operating system to allow crazy things to work that never should have worked, and are committed to maintaining that crazyness to keep old apps working on new versions of the OS. The problem with auto updates, is that Micrsoft isn't perfect in testing against all of the crazy workarounds they have in the OS, so each company really needs to be able to test and verify the updates first, to make sure it doesn't bork their computers.

Google doesn't have nearly as much craziness going on. Nothing on the scale of Microsoft. So, there is much less of a likely hood that they'll screw up my phone.

But conceptually, yes, giving a third party ( even the OS vendor) root access to update anything on the device is scary for security and privacy, I get that. I guess if you are already thinking you shouldn't trust google, you probably shouldn't be running Google Play Services in the first place, Stick to AOSP + Freedroid.