I'm terrified somebody will think their tweak is 'obviously safe' and share it online and before we know it a combine will run through an elementary school.
Using your line of reasoning, we should close down repair shops altogether. How can we trust people without engineering degrees work on something like brakes? Before we know it, we'll see buses full of schoolchildren on fire or something.
The fearmongering aspect of "combine running through an elementary school" aside (although perhaps the fact that schools aren't usually located in corn fields and have walls could warrant a reminder), I personally find the general approach of "I am afraid of X, so let's make/keep X illegal" terrifying.
I won't respond any more, since I'm pretty sure that's trolling.
People are generally pretty good at not putting questionable, critical parts into vehicles. Hopefully that holds for the software "part" as well. Maybe if software engineering moves towards better testing practices, we'd have reliable methods to test whether firmware was safe or not.
Many states already require vehicle safety inspections to address concerns such as yours. I could see states requiring manufactures work with the state to provide a way to inspect the firmware for safety, (not just checking the hash against the manufacturer code).