Yeah...but with any automation, the possibility of the autopilot doing something unexpected is always there. Most of the time we accept it because the allowable error tolerances are such that the deviation will not cause damage to property, injury or loss of life. When those allowable tolerances get narrower, additional controls (including the human ability to immediately detect the excursion and correct it before it causes a mishap) are required.
When traveling at highway speeds in close proximity to other stationary or moving objects (meaning withing a few feet), having your hands on the wheel and being able to detect the excursion through a tactile feeling (in the case of this accident "the wheel is starting to turn on a straight road to an extent beyond the normal straight line adjustments") and then immediately override it by gripping the wheel is exactly what I would think the expected driver behavior is..
It's kind of like when you are driving down the highway in a non-autopilot car with your hand just loosely gripping the wheel because the car is driving along straight. As soon as the car starts to slide towards one side of the lane or another, most experienced drivers grip the wheel more tightly and apply a little bit of pressure to counteract the drift immediately and, in many cases, subconsciously. I would suggest that for Tesla autopilot use in tight traffic at high speeds, this is exactly the appropriate behavior and the wheel nag system is Tesla's approach to trying to ensure people ARE keeping their hands on the wheel and monitoring. I'm less than thrilled with the current system as it actually penalizes people who rest their hands on the wheel but don't create detectable torque on it and would much prefer that there was some other (capacitive or pressure) technique used, but I can certainly understand their approach. I can also understand the increased nag policy given so many current user's propensity to go completely hands free and engage in truly distracted driving (reading, email, watching movies, etc.) where they are in no position to detect, let alone prevent, an excursion. Of course the Tesla marketing efforts and the way they demonstrate the current autopilot don't exactly help address/prevent this behavior either....