If you phone is hackable by you, what stops someone else from hacking it? Ultimately, it's a trade off between security and openness, and I think it's good that there are choices on both sides.

This comment is tricky because "hack" can mean different things in different contexts.

If I run software the OEM didn't authorize on a phone that I own and know the password for, that might be described as a "hack". Unless you're one of the horrible people trying to push OS-level DRM on everything, my doing that is a positive or neutral thing.

If a third party gets software that I didn't authorize to run on a phone that I own by tricking me into opening a malicious PDF, that's also a "hack". Almost everyone considers that a bad thing.

One does not imply the other.

Once you have used an exploit to get system access to your own device, you can patch the software to prevent anyone else from using the same vulnerabilities. See e.g. https://github.com/EolnMsuk/AntiDarkSword (but of course, as more and more vulnerabilities keep being found, it becomes basically impossible to backport all the fixes)