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Agreed. Two brakes - especially with skinnier tires - makes absolut sense for descending with a fixxed bike. And there is a difference between urban style fixed gear riding/racing and using some classic touring bikes while touring (load on the bike, maybe some rougher roads).
I realised a real difference when using my modern monstercross as fixxed bike, the traction of the wider tires is helping quite a lot when going down...
It's really perfectly OK to have two brakes and fixed - I certainly wouldn't be happy with only a front brake.
Why?
I certainly don't think a single brake for a fixed wheel novice is a great idea.
Of course, if you only use the bike for flat TT courses or riding round the Heathrow perimeter road, one brake should be fine.