It's not a strawman argument, it is a fact. Without the ability to audit the entire codebase of self-driving cars, there's no way to know if the manufacturer had knowingly hidden something in the code that might have caused accidents and fatalities too numerous to recount, but too important to ignore, that were linked to a fault in self-driving technology.
I was actually trying to find an article I'd read about Tesla's self-driving software reverting to manual control moments before impact, but I was literally flooded by fatality reports.