I'm not arguing against the update making the device slower. But the fact it's built so people would upgrade(via irremovable nagging), even when it's clearly not what's best for them.
Huh? Of course you're not arguing against the update making the device slower. You're arguing that the update not only makes the device slower, but that this is a deliberate action by Apple to make older devices slower. And I'm saying that's ridiculous since it happens to pretty much all software anyway and all Apple would have to do to make this happen is just develop updates the same way everyone else does.