> Hypothetical: if you modify the software in a Tesla, and your modification allows a hacker to remote control it, and this power is used to commit vehicular homicide, how much of the burden of responsibility do you have?

Hypothetically: a friend borrows your car, but you didn't fix the break fluid leak, and he runs over someone.

Who's at fault?

> With regards to phones however, I explicitly want the devices heavily locked down by law, to the extent that other people should not be allowed to put random software on them

that's the definition of a phone.

IMO Apple is to blame for creating the "smart" phones that can run arbitrary software.

They have created the problem that they are allegedly fixing by imposing walled garden on their users.

It is like handing guns to kids and then locking them up in their rooms so they are safe.