I don't disagree that you need to use both brakes at the same time in order to reduce your stopping distances. I mentioned that he "forget about the rear brake for awhile" in an attempt to get him more used to the front brake. In my experience, if the rider is used to using the rear brake on the street, then they will rely too heavily on that brake in an emergency situation. And "grabbing a handful of front brake" on one of our bikes is not likely to put you over the front or stand the bike on its nose. If you can do either of those, then you have some serious brakes on your old scoot.
Certainly there are isolated instances where relying on your front brake will put you on the ground, but in an emergency, when you don't have time to think but simply to react, I would hazard a guess that you are much more likely to hit the on-coming car if you are relying primarily on the rear brake to stop your bike. And motorcycles are not that easy to tuck the front wheel on. It takes much more than a piece of pea gravel or a little bit of sand. Granted, those will effect the stopping distance and occasionally you can lock of the front wheel, but if the wheel locks, then you back off the front brake. However, you don't learn that skill over night and it doesn't come magically when you need it most. As was mentioned, it's all about practice. And chose a controlled environment (ie that vacant parking lot) for your place to practice.
However, there are a lot of folks that will swear by the rear brake. All that I have to say is that we will have to "agree to disagree" on this one. In my case, I upgrade my front brakes, use HH race compound pads and forget about my rear brake completely. Yes, I've hit the ground a couple of times, but I've never plowed into the "I didn't see you so I turned left" car driver or the "I missed my turn so I had to hit the brakes" car driver either.
Those impacts will definitely hurt more than the occaasional front end tuck.
Tracy