I don't get how this happened. That must have been a difficult rail to put up. It's not like it was so quick and easy that they got halfway through it and realized they messed up. Once you're climbing the ladder while holding a heavy piece of metal, you should know that this is not worth the effort. There are no mythical giants walking around who will need this. Giants wouldn't take the subway anyway, especially the claustrophobic giants.
This is just asking for parkour dudes or stupid teenagers to mess with it. If I saw this I'd probably be compelled to climb my un-athletic self up on that rail and do something cool. You know what's not cool? Ending up in the hospital because you thought you were some kind of action movie star.