It's pretty clear that if a human can't even pay attention to a light directly pointed at them, we have a very long time to go before humans can safely drive cars without a computer to intervene when needed.
Of course, the road system is designed for humans' foibles, not computers' foibles, and computers will have to deal with that. But the bar is low.
Computers aren't really as consistent as you say, either. Obviously, a deterministic machine will produce the same outputs for the same inputs. But when your inputs are camera data from the real world, you'll never get the same input twice. For example, my car sometimes misreads or fails to read speed limit signs, but it'll usually read the exact same sign perfectly fine the next time I go past.
This is better for the environment, there is a lot of energy lost in a full stop for a stop sign that could be saved: less air pollution/CO2 to deal with.