A lot of stories resemble each other, but usually they aren't completely identical. For example, Stargate's time loop episode was approached as a comedy episode, showing O'Neall and Teal'c doing stuff they always wanted to do but would get in trouble for, and forcing them to do the intellectual work usually done by Daniel and Sam. Farscape's time loop episode was more of an investigative episode. Neither are anything like Cause and Effect.
Starate's "The Nox" is identical to Errand of Mercy. The humans land on some planet where they find a population of apparently primitive, defenseless natives. The bad guys are there with the intention of enslaving and murdering said natives. Said natives seem unconcerned. Turns out they are super-powerful pacifists who end up stopping them from killing each other and forcing them to leave.