Even if you say, "well, I could sell the Tesla rather than repair it," how many people are going to want to buy a broken Tesla? How do you explain to them, "It's totally mendable, I just haven't done that because. . ."? You'd basically have to tell them that they're buying a car that Tesla charges extortion fees to repair.
Even if you never want to repair your own car, even if you never want to go to a third party for repairs, you benefit greatly if you aren't single-sourced for repairs. Even if you will never take advantage of it, some other people will and, as such, Tesla would have to be competitive on price.
Second, this is not just about shade tree mechanics. This type of vertical integration means you have a sole source for parts and work if you buy a Tesla. Tesla can thus charge as much as their customers will bear without driving them to buy someone else's car. They have no incentive to pass supply chain or servicing efficiencies on to their customers. It's an arrangement the other car companies only dream of, which is why they keep trying to throw roadblocks in the way of third-party mechanics and parts manufacturers.
You'll find Apple apologists who will excuse this as well.
This is excellent for Tesla, but awful for the consumer.
If you leased the car for 8 years and then returned it, that wouldn't be so bad, but most people wouldn't want to pay the full retail price of a car only to have it potentially become a paperweight after 8 years.
Allowing the manufacturer to determine where you can service your car has been tried before and it ended badly.
That's the million dollar question.