I would not describe it as "parading" anyone anywhere, and it is not done "so that everyone can see them". It is usually the simple matter of taking a prisoner out of a police station and into a vehicle parked on the street in front of the station (because in older cities such as New York, which is where this took place, there often simply is no other way to do it; most police stations in New York do not have separate vehicle entrances.) If the press is aware that the prisoner is going to be transported, they will commonly wait outside the police station in order to get a picture of the prisoner being escorted to the vehicle by the police, and it is their right to stand on a public sidewalk and take pictures. I am not sure what sort of alternative the critics of the practice envision; we can't very well drive cars through solid walls, or catapult prisoners to court from the roof of the police station house, or demand that photographers not use a public street.
