Look at it this way: would you rather wait for five 9s against getting in a collision of any kind, in a car you won't be able to buy for another 25 years ... or settle for four 9s, and take delivery by christmas?
I don't know enough about the odds or the effect vs speed to comment with any confidence about whether Cruise's autonomous driving system fits this pattern or not, but I too often see a knee-jerk "slower and safer is always better when LIVES are on the line!" reaction, and I think it's worth being careful about whether it actually does make for a safer world.