You are dumb as a brick. You accidentally miss seeing a stop sign and kill someone, you have committed negligent homicide
There are certain things the law presumes, as a matter of public policy, that folks are always obliged to take note of, stops signs, red lights, etc. (unless obstructed by overgrown bushes, etc..). You accept that as a condition of your drivers license. That's not relevant to a mistake of fact defense scenario like we're discussing here.
