Tesla is not even assured of getting self-driving approved in lots of jurisdictions. It's going to be a long uphill battle to get it accepted. They are aware that even well-intentioned owners and modders could get into all sorts of trouble, and that the blame would fall on Tesla and self-driving cars generally, potentially doing great damage to their prospects. They're already under scrutiny.

If you buy a self-driving Tesla in the future, you do own it. Drive it anywhere you like. But the software is under license and may not be used for certain things. Demanding that they open up their software to interfacing with who-knows-what is to demand that they introduce new security measures and functionalities, dependent on unpredictable third parties with unknown properties.

Also, there's an easy way to avoid not feeling like you own your Tesla: don't buy a Tesla. I mean, as of now you really have to go out of your way to get one - so if they're "fucking over consumers" so bad with this, why would you buy it? This isn't something they're springing on you after a purchase, they're warning you years in advance.