Bike regulations are typically regional things in the US (and I suspect in other countries as well). Also, it is hard if not impossible to enforce these regulations on bikes (and are typically far less serious than car / truck enforcement), since its trivial to take the brake levers and what not off at home.
From my perspective, it is indeed ridiculously dangerous - even on a fixie, your legs may be too weak to stop using just the drive train, or you may need to do an emergency stop which would be quicker if you used another brake like a front brake or just run out of skill one day. With a single speed non-fixie (i.e. freewheeling is allowed), you don't have a way to stop other than your feet (or face) if you don't have at least one brake. On a fixie however, the resisting of pedaling does make a rear brake considerably less useful than a front brake.
As for the requirement of only a rear brake, the front brake is often viewed as a dangerous brake by most people who haven't cycled a decent amount, because they believe it will lock up the front wheel automatically and send you flying over the handlebars. Hence, the requirement being on the rear. The fact that it works for little kids bikes with coaster brakes as well is mostly a convenience.
The main thing is that it looks "cool" to have no brakes, ride your bike with no handlebars, etc. If they plow into someone else or hurt themselves because of it, its not really skin off my back (much like if they get hit by cars for riding at night with only reflectors). Theres only so much you can do to protect people from themselves, especially with something that can be so easily tweaked at home like a bicycle for this purpose.
As for people manufacturing bikes (for road use) with only one brake, I think bikesdirect sells some that way.
The only bikes which should have no brakes on them are possibly those used in a velodrome (i.e. track bicycles which are actually used ONLY on a track). [Here, it is actually dangerous to have brakes.]