If the user wishes to, they should not be limited to what is included in one particular proprietary “app store.”
If consumers wish to examine the low-level code that is running in their pockets, to check for invasions of privacy, run the anti-virus software of their choice, join VPNs, install firewalls, or just tinker with their operating systems, phone and device companies have no legitimate basis for preventing this.
If people want to install Linux on their iPhones, Boot to Gecko on their Windows phones, or just run a different version of Android on their Android phones, the company that sold them the hardware must not prevent them. Using a cryptographic bootloader to defend against malware is a fine idea, but there must be a way to reconfigure this security mechanism to (1) allow an alternative OS to be installed; and (2) to offer the same cryptographic protections for the alternative OS.
Apple denies warranty coverage to users who have jailbroken their iPhones. While nobody is asking Apple to support jailbroken or modified software, it is inexcusable that the company threatens not to cover, say, a faulty screen, if the customer has chosen to modify the software on their device.