I didn't read through the article but I think you are right - the author means that the car is a frivolous liability. This would mean that the car is expensive and has unnecessary features, is a bit of an indulgence, a luxury item (frivolous) and the liability probably refers to either the expense of running it or that there will be lots of problems to keep sorting out (possibly all those techno features).
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"Indeed, who could argue that it isn't a frivolous liability?"
This sentence essentially means that "this is a frivolous liability", correct ?
If that's correct, then it doesn't make any sense. I guess author wanted to say "it isn't frivolous liability"