Is it any different to the chaos that can be caused by a road vehicle breaking down in the wrong place? Or a plane conking out in the middle of a runway? Or a boat coming to grief at the harbour entrance? Where ever you have a transport system you have the potential for chaos if something breaks down in the wrong place.
There are six working platforms at Gatwick with a seventh about to open. That's like three runways or lanes in each direction. How can ONE TRAIN block six lines? I'm not saying it's Southern's fault necessarily but that is really poor design isn't it?