That's because you simply do not know how to ride a bicycle. In such a situation you need to get your weight back behind the saddle and modulate the application of the brake.
O.P. is one hundred percent correct that you do not need a rear brake -- and I speak as someone that rode for several years in without one including in SF.
I don't know how your particular weight is distributed on your particular bicycle or what, but you're spreading dangerously wrong ideas.
If you're going downhill and a child runs out in the street from between cars and you need to stop, and you're a normal person on a normal bike, you need a rear brake, end of story.
If you modulate your front brake to not lock up, that simply means you stop far too slowly, and hit the kid. Even at what seems like otherwise a safe speed, things (like children, or soccer balls) can run out in front of you at the last second and you need to stop suddenly.
You absolutely need a rear brake for safety. Just because you could get by without one in most situations doesn't mean you can get by without one in all situations.
"You should always apply the rear brake, and slightly in advance of the front brake, so that a slight skid at the rear will warn you if you get close to the hazard point at which the bike may tip."
"Flat asphalt is one thing, 30 degrees sloped rocky road is another. My hold is that in the second case the back brake is MORE important than the front brake."
"I myself got into the accident once. It happens so fast that you never have time to lean your body backwards and provide more tractions for the rear wheel like other have stated."
"Depending on where your center of mass "hovers" over your bike, you may need a different strategy."
"Having had more than a few over-the-handlebar incidents back in the day, there is no situation in which I would ever even consider using only the front brake again."
"On the road bike you are alot lower and therefore don't go over the front quite as quickly."
"If you learn to move your weight back (ideally behind your saddle) during strong braking then going over the handle bars is nearly impossible (except under very steep hills)." (Note the "steep hills" part, which is my whole point about safety.)
"On mountain bike, the momentum partly transferred to seat and pedal as a result from a more up-right pedalling position. Remember that your body is about 3-5 times the weight of the bicycle, and they are on top of the bike. So the higher you are from the ground, the easier for you to toppled up."
[1] http://bicycles.stackexchange.com/questions/10918/do-skilled...
[2] http://bicycles.stackexchange.com/questions/25856/why-do-we-...
It would be refreshing if you were able to demonstrate a capacity for admitting that perhaps you have something to learn. I would advise taking a mountain bike class and coupling it with something like the U.K.'s Bikeability or the U.S.A.'s League of American Bicyclists equivalent.
I fear, instead, that you will spend your time hectoring internet strangers about the dangers of bicycle riding based on your own incapacities and incapabilities.
Good luck.
If you're going down a hill and you need to do an emergency stop, the back wheel won't do you any good. The rule of thumb I was taught was that the back wheel will only provide 1G of deceleration, under ideal circumstances. If the road is wet, or there are leaves, assume less.
If anything, the rear brake can be used to slightly pump up the front fork, which allows the front wheel to find its own way through mud/leaves/snow. Basically, apply a touch of rear brake when you go through a slippery curve, squeeze the frame between your thighs, and let the bike find its own path.
If you take into account that during braking, and even more so during an emergency brake, all the inertial weight lies on the front wheel, it makes a lot of sense that the rear brake is so useless.
In France, bikers call their passengers "SDS," which stands for "sac de sable" (sandbag). Very useful to increase grip of the back wheel when accelerating strongly. Not when braking.
I've actually faced the "child jumping out from behind a parked car" before, and I passed that test. When I jammed hard on both the front and rear, both tires locked, the rear tire swung around the side until even with the front (at that point it was no longer behind the COG so it rotated down instead of up), and I twisted my back foot to unclip and stomp. I looked at her, she looked at me, then she ran on across the street. Glad I wasn't driving a car!
http://www.bikeforums.net/tandem-cycling/52661-shaving-arai-...