If a company builds an electronic device to be used on the consumer market and they do not want the consumers messing with the hardware, they put their own software on it but then say the software is licensed, which prevents the hardware from being messed with because to mess with the hardware has a tendancy to affect the software and because the software is only licensed it means it comes with a lot of restrictions.The point is iOS isn’t yours to do as you please. You license iOS from Apple. This is something you agree to the first time the device is turned on. You also have 7-14 days to return the device back to Apple for a full refund, no questions asked if you don’t agree with the license.
iOS has never been sold separately, is not open source or public domain and doesn’t belong to the user. It is licensed and by agreeing and continuing to use it, you are bound by it’s subsequent limitations, that you agreed to.
You absolutely can decide what you do with your device, that does belong to you. You are free to throw it in a lake, free to run over it with your car or free to give it away. If you have the expertise and want to install another OS, you are free to do that too. Apple is under no obligation to make it easy for you to do so however.
The problem for Apple is that in some cases their licensing terms and conditions mean nothing, especially when it can be proven that a persons intention is just. The classic case in point being iphone jailbreaking which Apple fought heavily against using the iOS licensing T&C's as to why jailbreaking should be illegal but the courts went against Apple and said it was legal for an iphone owner to jailbreak their iphone.
Just because a company lists of a whole host of terms and conditions for it's hardware and it's software, it does not means these terms and conditions will hold up in a court of law and many times this has been the case.
So please, enough with this 'iOS is not yours to with as you please' nonsense.