I ride every day to work on platforms, 1 mile each way, and I go home for lunch. And I ended up doing 12 miles yesterday on my fix geared too cause I was bored and didn't feel like going back for my road bike. Guess if the gearing is too low you'll spin too much on the downhills and that can get dangerous, but I have 48/16 gears and am fine most of the time.

It definitely not a good idea if you're starting out with platforms though...

And platforms with no brakes? Thats insane...