Except that the comparison isn't:

320,000 people dead due to traffic fatalities over 10 years.

  vs

350 people dead in terrorism over 10 years

It's:

320,000 people dead due to traffic fatalities over 10 years causing little political fallout.

  vs

350 people dead in terrorism over 10 years plus a lot of political fallout for each event.

Bluntly, to shift the risk argument we'd either need to take politicans out of the decision making and give it to some independent fact-based body, or get the media and people in general far more riled up about car crashes.