Your argument is not totally unreasonable - but not within industry norms. Also Tesla is the manufacturer for electric cars in the public's eye, if they get a reputation for unreliability it will set the technology back decades. (see the Oldsmobile Diesel engine from the 80's)

So for a variety of reasons, I'd argue they have a moral responsibility to fix it, INAL, so it's unknown to me if they have a legal or regulatory responsibility too.