It makes me uncomfortable too. I think it's because it's a real world trolley problem.

We all make similar decisions all of our lives, but nearly always at some remove. (With rare exceptions in fields like medicine and military operations.) But autonomous vehicles are a very visceral and direct implementation. The difference betweeen the trolley problem and in autonomous vehicles is in time delay and the amount of effort and skill required in execution.

Plus, we're taking what is pretty clearly a moral decision and putting it into a system that doesn't do moral decision-making.