Autonomous cars are on the roads today. They're a ways off from serving as reliable truckers or taxis, but that's in our future. We're seeing rapid advancements in machine learning, especially in computer vision and abstract strategy games.
Trucking alone accounts for 5% of the US GDP [1], and employs 1.7 million Americans annually [2]. That's about 1/10 of the total US workforce. Taxi drivers and support staff for trucking are smaller occupations that are also at risk. What happens if all those jobs disappear overnight?
Hopefully the people in those jobs will successfully transition to other careers, as many did after the industrial revolution. But it might not be pretty in the short-term. I don't think it's irrational to be concerned about this.
1. https://en.wikipedia.org/wiki/Trucking_industry_in_the_Unite...
2. https://www.bls.gov/oes/current/oes533032.htm
aside: Wikipedia has some nice graphs, but shouldn't be considered reliable. What's the best source of economic and labor data in the US (or other advanced economies), aside from Bureau of Labor Statistics?