Riding fixed with no brakes ain't so bad. Kinda crazy in traffic, though. You can slow down a bit by resisting the pedals rotation. You can slow down a little quicker by skidding. You can slow down even more quickly by jamming your shoe behind your fork or dragging a shoe on your back wheel Ted Shred style.

Single Speed without brakes is what's really crazy. I've had a few single speeds without brakes for short periods of time and braked Flintstone style (if on a low-saddle bike) or foot jammed behind the fork depending on how urgent the stop was.

I don't like fixed downhill either, but other than that they're fun as hell to ride.