That fixie case was silly. Everyone got all hung up on braking distances and him lacking a brake, even though the distance over which he would have had to stop was tiny. If he’d met the legal requirements for brakes she’d almost certainly still be dead but there wouldn’t have been an open and shut way to throw the book at him. That being said, riding around on an illegal bike like that is stupid, like driving your car with bald tyres and terrible brakes - you’re an accident waiting to happen.
Mind you, even then, the laws on brakes are weird. If your saddle is less than 635mm from the ground then you only need one brake, so if you’re riding a BMX with the saddle way down then I think you’d only need the one brake.