Oh I definitely understand that the vast majority of touch screens are utter trash! But that's not to say that all are.
Understanding what lane I need to be in, and what the traffic conditions are up ahead around the bend; these things add to situational awareness that makes driving safer. But I'm just not going to use a shit GPS that I need to program an address by spinning a scroll wheel and individually selecting letters.
If you had a large touchscreen in your car, you wouldn't have to look down at a tiny phone screen to see these things. They would be in your peripheral vision and easily checked without losing track of the road.
Now I regularly move to the right and slow down long before approaching a traffic jam on the highway, versus the typical hard-brake when the traffic comes into view.
At an unfamiliar complex intersection (greater than 4-way), sometimes you can't figure out where the GPS wants you to go. A quick pinch-zoom before the light turns can give you the visual queue you need to avoid having to make a last minute decision as you enter the intersection. That's totally possible on the TM3 because it's instant, smooth, and fluid (and it's really great at automatically zooming back out to the right level as you start driving again).
And to give another anecdote, today on my drive home navigation was set to take me 'Home' (by the way that's two taps on the screen, and takes less than 1 second to activate as soon as you sit down in the car). I was on the highway in stop-and-go traffic with AutoPilot. My wife called and asks me to pickup takeout. I know it's too early to order, and traffic is terrible. I need to know how long to wait to order, so I tap the steering wheel control and use voice control to change the destination. Because it's internet connected, I can just speak the restaurant name and the town. It tells me the traffic-aware arrival ETA so I know when to place the order, and adjusts the route (taking an earlier exit). Unfortunately there's no single tap on screen to make the call - POIs don't have the phone numbers listed (yet)!
So I find that there are plenty of perfectly appropriate reasons to adjust navigation while driving, I just think very few people have experienced how a proper large touch-screen implementation can supplement and enhance your situational awareness and allow you to complete tasks safely and efficiently while underway. The is strictly better than the real-world alternative which is for people to try to complete these tasks using a phone-in-hand while they are also attempting to drive.