Here's my opinion.
If duplicate answers arrive within moments of each other it's not really that surprising. It's the fastest gun in the west syndrome and very similar answers are bound to occur.
However an identical answer several days earlier like the one found herehere I consider a problem. In this case it may simply be that the user requires some guidance on using the site rather than the blatant rudeness it appears to be on the surface. I do think late identical should be deleted in favor of those that came before them, however similar answers that are more cohesive or fully formed should be left to the voting process.