Earlier quoted context omitted.
Restarting from a full stop requires good pedestrian awareness. In city traffic, there might be people crossing in front of the car when it's stopped. Restart also requires getting the driver back on line. They're probably on a phone. That's why some driver input to start motion is desirable. The user interface problems for automatic driving are very tough.
I don't think the parent was talking about restarting from a full stop, it looks to me like he was saying that his car's radar-cruise system won't actually stop the car in heavy traffic, so if you're not paying attention and don't brake manually in time, you could rear-end someone.
The problem with the system is it's relatively simplistic. You set a following distance (there are 4 options) and the car will never get closer to the car in front of you than you've specified. It will slow down as necessary to maintain that distance.
This works fine on empty highways but in traffic it doesn't help. Since it won't go to (and resume) from a full stop you have to fiddle with it constantly. In tight traffic the distance has to be modified or people will continually jump in front of you (causing the car to slow down and back off).
I'll also say that it waits a surprisingly long time to start braking to the point it can be a little unnerving at times. I know it knows there is a car there (there is a symbol on the dash to show that it sees a car) but it doesn't act until you get much closer.
A system like Tesla or Volvo have that can bring the car to a stop and then speed back up or could decide to try to maintain a distance similar to that other drivers are maintaining would be much nicer.
Still for long trips the Honda system is great. And you can always put it in 'dumb' cruise control mode if necessary.