You make an incredibly good point - whilst any safety improvement at all is obviously and unquestionably a good thing, we can take this opportunity to step back and analyse the situation we've found ourselves in, and decide that the status quo is far from good enough and we should in fact be aiming to do much,
much better.
A convenient advantage of regulating for self-driving vehicles is that we can put minimum safety standards into law quite easily, and enforce them meaningfully - because the prize for reaching and adhering to those standards is so great for the players involved, and because we have a relatively clean regulatory slate because of the clear step-change in the technology.
As well as the most important factor, safety, it could also be possible to step back and consider the other disadvantageous side-effects of the current status quo with cars, particularly in cities - noise, traffic congestion, wide roads with thin pavements/sidewalks for pedestrians, indeed a general culture of cars having priority over pedestrians in various situations where the number of pedestrians is much greater than the number of people in the cars.
These are all things which, depending on the city and the culture, can be really significant problems and which I'm sure would never be tolerated had they not crept up on us over decades. Regulating both for and with the capabilities of self-driving vehicles might give us opportunity to vastly improve the status quo in these areas, too, in a relatively short period of time.
It could be quite important to take advantage of the opportunity to realise such optimistic targets now, starting green field, as it can only get more difficult and become much slower to implement after the first set of regulations has been put into effect.