there is a never ending argument with this question. it all comes down to track bikes are not meant for the street. therefore no need for brakes, because they are meant for velodrome use. the point of having a fixed gear is for simplicity. i used a front brake for the first week, learning how to go down hills, and go fast. now i dont use brakes, and i go faster than my friends on road bikes.

but really, its just a choice that only should matter to yourself. who cares if you have a brake or not. its your bike.