I also want to run the software of my choosing. But there’s not a single phone you can completely do that with. Some of this is due to design decisions, some of it is due to corporate lock-in, and some of it is due to regulatory requirements.
I wouldn’t be against a law requiring side loading and unlocking, I would be in favor of it. This only addresses part of the software on a phone, though. There’s a lot of software on a phone beyond user space applications.
But I do think it would be reasonable to put some hurdles to make it difficult to do. There are completely valid reasons to protect the average user from being scammed by malicious software.