Car bombs are bad, but they are not "WMDs." Nevermind that it is cheaper to find a suicidal driver, or trick a driver into going on a suicide mission than it is to buy a Tesla and hack it into a car bomb.

Many imagined terrorist threats are threats only in a vacuum. A rifle and a tall building resulted in 50+ deaths and 500+ wounded. Any technologically complex attack has to beat those numbers.

The only notable attack with an actual WMD was the sarin gas attack on the Tokyo subway. It killed about one fourth the number of people as a man with a rifle in Las Vegas. It took a secretive cult organization to implement. That's why nobody uses WMDs for terror attacks.

Trucks and rifles do enough damage without even having to acquire bomb-making skills. Autonomous vehicles that are programmed to avoid hitting pedestrians are likely to make it harder to use vehicles as a weapon, not more deadly.