due to the laws of physics, when you brake, weight is shifted forward reducing the effect of the rear brake. this is why cars and trucks generally have much larger brakes on the front, why Campagnolo uses dual pivot on the front and single on the rear, and why motorcycles have two front brakes and one rear.

i think most studies show that front brakes make up something like 70% of braking capacity. (depending on the "vehicle")

if you are going to sell your braking ability short by only running one brake, why not keep the more important of the two?