Second hand Teslas represent a challenge as someone pointed out. You also can't necessarily modify or inspect the car without Tesla getting their panties in a twist (I dare you to connect to the network inside your car and try to get access to the onboard computers and then try to have the discussion with Tesla about who's car it really is).

The there are the massive privacy issues and the fact that you can't do anything about that: your car is spying on you. (I know consumers don't care enough about this in the US to elect politicians that take privacy seriously, but in Europe we do. Which is why Tesla is under scrutiny for not only collecting massive amounts of invasive data, but also for not being able to adequately safeguard the data they collect).