I think Gursky uses multiple exposure to increase the density of crowds and to create color patterns. His work is appropriate to art venues like galleries and museums. It's not presented as "documentary," so anything is fair game. The visual effect comes first.
If the _LA Times_ photo were part of an exhibit at a modern art gallery called "Stagings of Violence" or "Dangerous Compositions," where it was understood that the photographer was creating semi-fictional scenes to tell a dramatic story, then it would be unobjectionable.