I can think of many scenarios in which this can be actually dangerous. Not all roads in the world have a side lane in which you can stop at any time. Driving with a foggy windshield waiting to find the proper lane can be very dangerous.
That sounds awful. When you’re in lane 3/6 on a highway doing 85mph… “oh shit my window is starting to fog up, lemme try and navigate my way to the shoulder with my quickly diminishing visibility so I can press a button then try and merge into a busy highway from a standstill”.
Just design the vehicle better. I can see the status of my HVAC without taking my eyes off of the road—it’s on a display mounted on top of my dash, forward toward the windshield—and turn on defrost mode with the press of a single, large physical button inset inside a large knob which provides a clear touch cue.[0] I have never had to take my eyes off the road to adjust any of this system.
You picked a bad example. Defroster is one of the safety critical controls you need to be able to turn on now. More than once I've crossed a weather front while driving and the outside humidity and temperature have both changed drastically causing an instant need of change to the HVAC for safety reasons.
The radio should only have minimal accessible controls while driving. However even then remember that the non-driver should get the ability to have more control.
If you need to turn on the defroster, pull over, turn on the defroster, and pull away again.