If you drive your manual car real fast and then accidentally flip into reverse gear you'll pretty much instantly destroy the gearbox. How many other tools do you use daily that have such a dangerous and expensive failure mode that isn't protected by anything, huh? Not many. These things are dumb.
@stefan many cars have it where a sixth gear would be. Yes there's usually a lock on it, but you could easily hit the unlock accidently.
@sixohsix Sure, but from gear five to six, you would just pull the gearstick back. For reverse you had to slide right first. Moreover you had to pressure it in, since the gearwheels are moving the other direction.