I respectfully and strongly disagree. What you are forgetting is that these are connected devices and that hacking them can have significant consequences. If you knew there was a vulnerability that anyone from the internet can take over your car (or simply plant malicious software that will do bad things), would you like the car manufacturer to patch it or leave it open for you to fix yourself? If your car wakes up at 4am and floors it into your living room, will you claim Tesla's fault, or admit that you should have found this vulnerability yourself and therefore take full responsibility? What if your battery deteriorates so you get only 20% of original range but Tesla says "there is evidence your car was hacked, therefore the battery was possibly operating outside of the safe range, so you're on your own" - would you agree with that?
Patching security vulnerabilities in connected devices that can be turned into weapons should be mandated by law. Worst case scenarios include zombie cars that drive around hunting pedestrians. Sounds like science fiction? Current AP hardware was designed for the car to drive without a driver, malicious software simply ignores the "on private property" part and changes "avoid pedestrians" into "target pedestrians". It doesn't have to be bug free or working on most cars, even if 10% of all Teslas manage to kill someone while the other ones crash into things because the software wasn't perfect, that is still a lot of damage. Software defined cars are computers on wheels, the difference is the damage that can be done if they are compromised. Would you trust a public Linux distribution connected to the internet to control a heart pacer in your heart that has test modes that can kill you by inducing a heart attack? You get full source code to the Linux OS of course, so you feel confident you will never be hacked?
Bottom line is that yes, there should be a way for you to tinker with your own car, however the old mindset of "as long as it's mounted on a chasis of a street legal car, then it's street legal" needs to be changed to "as long you pass all the safety test a car manufacturer needs to pass" they you are street legal. Those tests should include security analysis of your car, at your expense of course.
Lastly, you are able to disable all patching today if you desire. Simply open up your dash and erase all the car keys, so that the car will never be able to connect to Tesla VPN for an update. You void your warranty, but you said you were good with that in exchange for software control. And yes, your warranty should go out the window the second you get any software control, as now you can operate the component outside of recommended (warrantied) conditions and there is no way for you to prove you didn't. Heck, by not patching you may be straining a component (say Tesla finds there is software bug that kills the battery cells, by refusing the patch you willingly are damaging the battery).