Because corporations maintaining such control over what should have been our computers is fundamentally unjust. It turns us into serfs of their digital fiefdoms where they make the laws and collect the taxes and tariffs.
Well you should be able to. If the customer is powerless to stop it we're going to see cars and fridges playing ads at full volume very soon.
Someone doing something bad doesn't excuse someone else for doing the same thing.
Historically, women couldn't vote, does that excuse countries that prevent women from voting from doing so, too?
Why should we give a shit about historical norms? For most of history most children died at childbirth. Does that mean we should accept a >50% infant mortality rate?
Are you new here? All of these things are examples of locked down ecosystems that most of us in favor of this change also want unlocked.
The idea that you can own a device and can't do whatever you want with it is asinine. If you can't do what you want, you don't own it.
Also, if you buy an Xbox, Tesla, Fitbit watch, fridge, etc. you can’t load whatever you please, either. Why would all smartphones be different?
If you look at it historically, the PC is about the only device allowing that kind of user control.