You can get by with only the front brake, but I do not agree at all that "expert riders use the front brake almost exclusively." The only time using the front brake alone is safe, much less advisable, is when you are stopping in a straight line on dry pavement.
Braking with the front is safe, including trailbraking, and most effective. Go watch motorcycle roadracing and tell me why they didn't all crash in the first turn. The rear brake is only used to square off the turn so you can get back on the gas more quickly.
I understand that the front wheel provides most of the stopping power. I don't dispute that. My argument is that you lose too much control over the back of the bike. When braking with only the front brake in a turn, the back two-thirds of the bike wants to rotate using the headtube as an axis.
If you are braking hard enough to unload the rear wheel the rear brake would be absolutely useless anyway.
Having seen enough people take head over heels and bike on top of them spills i will never ever use my front-brakes unless i am already using my aft brakes and its not enough. Even then i will apply the front much lighter then the aft.
They apparently don't know how to use the brakes properly and should seriously practice. Emergency braking is something everyone should be proficient at.