In theory, I agree with your viewpoint. Yes, obviously, safety critical systems need to remain safe, and a workshop that isn't capable of performing maintenance to the degree mandated by the train software shouldn't be doing it at all.

That is not the case here.

If that was indeed the case, one would expect the train's diagnostic systems to report that it has detected certain issues that need to be resolved before the train will start up again. But that didn't happen, instead the train simply refused to start, no error codes, nada.

Not only that, but further investigation revealed that the train's firmware contained code that would disable the train if it was present in a competitors shop for a considerable time.

> There should be an opt out system

This mechanism for disabling the trains, was never mentioned in the discussions or contracts for purchasing the train (which is why a third-party could win the repair contract). There was never an option presented to "opt out", that is why people are saying that the trains were sabotaged.

> to what extent is that Tesla's fault?

It isnt. You made unsafe modifications that can be clearly shown to have caused damage, it's your liability.

> Say Tesla made all reasonable steps they could take to detect third party mods and refuse to start the car, do we hate them too?

Depends, did their software present an actionable error or not? If the car gave an error code, and you look in the manual and it says that too much current is going to the motors (idk), and then you fix that and the car starts? Great! But if the car just refuses to start without any indication as to what is wrong, and further even if all repairs are reversed it still no longer starts? That sounds like deliberately sabotaging third-party repair.