I don't agree with Apple having the right to restrict software. As I said, when you buy a device, you are doing two essential things.
1 Purchase of the physical device. This is now your device. it's not a license, it's not a lease, you own it. Thus, property ownership tends to come with it certain rights for what you can do with the physical device itself.
2. Purchase / lease of the software on that physical device. This being the limited license.
in my opinion, the 2nd part of the transaction should not override the first part. if I chose to open myself up to malware, security risks, etc, on the physical device I own, than that should be entirely my right. Risks of that also my own should something happen (if I brick my phone installing a 3rd party OS for example, I believe Apple should have the ability to deny warranty repair)
In addition, Malware doesn't just "spread". these aren't the viruses of the 80s/90s, where just inserting a disk will infect a computeres MBR. Malware today still generally requires user interaction in order to install their payloads. Me installing malware on my computer will not infect my neighbour or vice versa. Same with phones. Should you install Malware on your phone, you might have security risks yourself, But your friends and families phones don't suddenly become infected either.
In the case of iOS restrictions, I would like to see device manufacturers be forced to allow for the replacement of the OS with a 3rd party OS if the default OS does not meet the requirements of the purchaser. Don't like being restricted to the App store only? Install a 3rd party OS that has the opening you require.
Now, That also doesn't mean Apple must support 3rd party OS's. That's sillyness. But they shouldn't be able to block it either. (This is also true for the rest of the computer industry that is doing it's best to follow Apple's lead and lock software to hardware)