The point is that, according to the law a sit stands, a device manufacturer that knowingly ships a device that can be used to accidentally jam communications is breaking the law. Not only is the device manufacturer allowed to modify the device to prevent this, they are compelled by the law to take reasonable steps to do so. Automatic updates are such a reasonable step (and note, you can refuse to install updates on your Android phone - of course, you'll miss out on security updates as well, and may not be able to run certain apps if you're too far out of date). The exact same thing is true of cars.
If a car manufacturer realized that they accidentally left a button in your car that allows you to leak oil, they would have to issue a recall, and any service shop that worked on your car would be obligated to remove said button to make your car work - at the auto maker's expense, of course. The service checkup is the equivalent of the online update on your phone: you're not forced to do it, but many things will stop working if you do, and illegal features will be removed from your car at the checkup.
Of course, I agree that the patch here is not at the same level as an easy way to accidentally jam nearby radios. However, the general legal principle is the same: the argument "Google can't legally modify my property in ways I don't want when I install an update" isn't true, because they can and should have this power in certain cases. That the particular case of enabling VoLTE despite the carrier settings disallowing it doesn't warrant this power simply means that this case should be fought by different arguments, not by a general principle that simply doesn't exist in law.