While some of the examples like the Dinan S1 M5 is legit, these companies are less of a concern that the average script kiddy who wants to "hack" his car because it's the new thing to do in town. Advanced features like traction control and even cruise control on vehicles are critical to implement perfectly, and a small mistake in the code that guides these can be fatal. Companies like BMW spend millions on testing the code and making it perfect for use, and what this article is arguing for is replacing that with something that anybody can write. This is not safe.
On the other hand, some things like the Nismo and it's software imposed speed limit are just state restrictions. The Nissan GTR has a set speed limit which is turned off when the GPS detects that you're on a racing circuit.
Companies are ethically obliged to make sure that no amateur or third-party can make their cars unsafe. They are right in doing so, because at the end of the day they are liable. If there is a fatal accident of a BMW M5 due to a software failure error, nobody (read, the media) is going to blame Dinan. BMW takes the brunt for it. They are blames for writing "shitty software".
Unless companies or individuals are legally obliged to be accountable for the changes they make to a car, companies are right in making the cars impossible to tweak. It's not about the fact that you "own" the car and hence should be allowed to do whatever you like. That works only for iPhones and Play Stations where your actions probably wont result in somebody dying.
tl;dr — Much like spare parts, faulty software can kill onboard passengers in vehicles. While hacking sounds "cool", slight irresponsibility can end badly.