Well, the button is already dedicated to turning off the screen and on previous iPhones, holding it down gave you the option to turn it off.
Now, holding it down brings up Siri, which now dedicates a button to a function I literally never use. I shutdown my phone at least once a month, whether that’s to do a simple restart, while at a no-phones event, or to save battery.
Now, you have to hold down the power button and the volume button to not only turn off the phone, but to access emergency SOS. If I’m in an emergency situation, I might not have the dexterity to do that with one hand or both hands free to do it with both. I have to use the latter considering how big the phones are now (iPhone X). My one hand is big enough to hold both buttons at the same time, but I need the other hand just to get the one in the right position.
