Earlier quoted context omitted.
People who argue that phones are computers are arguing the nature of a thing is its identity. It seems you are arguing that the intent of a thing is its identity. Using your argument, if I wrap my desktop PC in a cardboard box with holes for air inlet, air exhaust, and the power cable, and call it a heater, it's no longer a computer, despite having all the bits inside that a computer would have. I'd much rather decid…
You contradict yourself a little bit. If you decide your PC is a heater, well, then it is one! It is commercially unviable to sell it to someone third as that, but if you managed that feat, it would be a bit strange if this person then came to you: "You sold me this electric heater, but I looked into it and it is warmed by an especially hot Intel CPU. So I decided it is a PC and despite you are being in the heater-se…
That's a different issue. I support the manufacturer saying "we won't guarantee our computer-as-heater will work if you change the software."
What I don't support is "we have have made it legally/physically/cryptographically impossible for you to use the thing you bought however you want to."
If I sell you a watermelon, I'll guarantee its freshness. I'll not guarantee its fitness as a boat anchor, but if you want to try that, go right ahead.