Self driving cars are both defense and security related.
Beginning with the simple workflow:
1. Get many burner phones for cash.
2. Get many prepaid credit card for cash.
3. Sign up for many self-driving car services.
4. Targeted denial of service.
(I'm avoiding the very-slow-cruise-missile scenario because nobody wants to think about it.)
It used to be really easy, but law enforcement is cracking down on the ability to buy and activate these anonymously for obvious reasons.
Are there ways around these? Sure, but it's not nearly as easy as you're proposing.