>> I'm skeptical that driverless vehicles can factor in all the ways in which someone might maliciously cause accidents or damage to these vehicles

You're probably right, but as long as it doesn't happen frequently and there's no way to mislead sensors en masse, it's not a big deal.

There are malicious ways to cause accidents with current-day technologies also. e.g. Park a car in front of a train, fly a drone into a plane, etc.